Introduction

In light of the rapid and mandatory shift to online learning due to the pandemic, emergency remote teaching (ERT) evolved (Bozkurt & Sharma, 2020; Hartshorne et al., 2020; Hodges et al., 2020). Emergency remote teaching is a temporary shift in instructional delivery due to a crisis (Hodges et al., 2020; Moorhouse & Kohnke, 2021b). The emergence of ERT has necessitated continuous improvement and support for all stakeholders in the education sector (Tafazoli & Meihami, 2022), including teachers, which can be offered via OTPD courses (Hartshorne et al., 2020). OTPD refers to courses, workshops, or learning modules delivered online for teachers (Powell & Bodur, 2019). It should be apparent that online learning is no longer a stopgap solution but an essential component of education (Hodges et al., 2022; Kessler, 2018; Kohnke & Moorhouse, 2022). Furthermore, empirical evidence supports the notion that teachers are unprepared to work across online modalities (Bartlett, 2022; Crompton et al., 2022; Reich, 2021). Online or blended experiences are becoming part of some teacher education programs, but they are confined to pockets of innovation (Mouza et al., 2022). Thus, all teacher education programs must prepare teachers to experience a variety of online modalities (Ge & Huang, 2022). Hodges et al. (2022) envisioned that all teacher education programs will prepare candidates to be successful teachers in different online modalities by 2025.

This study undertook a small-scale qualitative case study of thirty Iranian English as a foreign language (EFL) teachers who attended a CALL professional development course. The growth in OTPD opportunities for teachers prompts us to question how online modalities like synchronous, asynchronous, and bichronous online learning can improve teachers’ CALL pedagogical knowledge through project-based learning (PBL) activities (Hirschel & Humphreys, 2021; Raes et al., 2020). Although bichronous online learning is emerging rapidly as a research domain (Martin et al., 2020, 2023), little is known about its implementation to develop teachers’ CALL pedagogical knowledge (Mendieta & Barkhuizen, 2020). CALL pedagogical knowledge is an understanding of how computers can be used in teaching languages (Hubbard & Levy, 2006). Inspired by Hubbard and Levy (2006), evidence of CALL pedagogical knowledge includes digital technology use, technology-enhanced material selection, development, and assessment. The findings are crucial to successfully designing and delivering CALL OTPD programs. Any empirical evidence is of the utmost importance to prepare for a future crisis that may require ERT (Bozkurt & Sharma, 2020; Erarslan, 2021; Mishra et al., 2020). If stakeholders inform themselves of the potential benefit of synchronous, asynchronous, and bichronous online learning, there will be great potential and many possibilities for furthering educational opportunities. Guided by this notion, the proposed research question is

How does teachers’ CALL pedagogical knowledge improve across synchronous, asynchronous, and bichronous online learning?

Literature review

Context of the study

As an emergency response to the pandemic, Iran, the context of this study, followed the lockdown and social distancing regulations and closed all educational institutions. Therefore, educational institutions suspended in-person classes and required teachers to teach online. To maintain Iran’s traditional education system, deficient and unplanned online education was imposed. In Iran and around the world (Metscher et al., 2021; Moorhouse & Beaumont, 2020), the online mode of instruction was new to many teachers and students. Accordingly, Tafazoli (2021) argued that this provisional and conditional transition could not be called ‘online education’ because online education is driven by well-chosen, well-prepared, and meticulous instructional design strategies. Hence, the sudden transition to ERT caused difficulties for most teachers in developing countries, like Iran. Therefore, due to the pandemic’s forward-looking effects, the Iranian education system should migrate from provisional ERTs and conditional responses and adopt a high-quality online education system (Tafazoli & Meihami, 2022). In higher education, online teaching will likely grow beyond the pandemic because it allows students and teachers to interact in real time while maintaining the flexibility of online learning (Moorhouse & Kohnke, 2021a).

Therefore, according to Tafazoli (2021), CALL teacher education and professional development are essential steps to move away from ERT. Enabling teachers to rethink their teaching practices and incorporate educational technologies into their plans involves the involvement of teachers in the evaluation, planning, and application of educational technologies. Teachers must rethink their teaching practices to enhance learning in online and blended contexts beyond ERT. An effective online learning environment must be able to take advantage of the affordances of a digitally rich environment and design learning experiences that are pedagogically sound. Thus, through professional development courses, teachers can move away from ERT and take part in evaluating, planning, and applying educational technologies, enabling them to rethink their teaching practices.

Online teacher professional development

The literature shows a growing need for professional development (Hubbard, 2018; Wasserman & Migdal, 2019), specifically technology-focused professional development (Kessler & Hubbard, 2017; Kohnke, 2021; Wang et al., 2020), as teachers must face new teaching and learning environments, including synchronous, asynchronous, bichronous, hybrid, and flipped (Healey, 2018; Kohnke & Moorhouse, 2022). OTPD has many advantages, like access to flexible, cost-effective, and high-quality professional development without geographical and time constraints (Elliott, 2017; Powell & Bodur, 2019). The potential benefits of OTPD for teachers include the development of knowledge by connecting them with a global community of peers with the same professional learning goals who share resources and ideas (Appova & Arbaugh, 2018; Kohnke, 2021). Professional development within online teacher communities’ fosters peer-to-peer support and interaction (Lantz-Andersson et al., 2018; Philipsen et al., 2019). Researchers believe OTPD courses could contribute to teachers’ professional development (Kessler & Hubbard, 2017; Lockee, 2021; Wang et al., 2020). Celen and Seferoglu (2020) used an OTPD course to enhance teachers’ technological skills. There was a consensus among participants that the OTPD was compatible with their interests and needs. The results of the t test also revealed an increase in technological skills. Thus, OTPD contributed to teachers’ development and teaching practices by improving their technological skills and knowledge. Also, Mohammadi and Tafazoli (2022) developed an OTPD course to support teachers’ reflective skills. Through an online course, teachers received practices that improved their reflective skills. Riel (2020) found that creating projects and participating in online discussions benefit teachers. Furthermore, Mai et al. (2022) developed a free 20-h OTPD course for English teachers to support their technological skills. Through modeling, the trainers demonstrated the interplay between technology, pedagogy, and content to participants and influenced their technological development.

Nevertheless, the sudden transition to ERT caused difficulties for most teachers and teacher educators (Bond, 2021; Hartshorne et al., 2020; Hodges et al., 2020; Mishra et al., 2020). Many teachers had acknowledged that if their classes had made better use of technology before the pandemic, they would have felt more prepared and suffered less stress when it struck. Moreover, Bartlett (2022) found that teachers experienced chaos and exhaustion and perceived that they provided less content to their students and had reduced interactions during the pandemic. Also, Trust and Whalen (2020) interviewed 325 teachers about their emergency remote teaching needs during COVID-19. According to their findings, pre-service teachers must be prepared to teach in various formats, settings, and situations by developing online and blended teaching competencies. Hence, Juárez-Díaz and Perales (2021) strongly recommended that teachers receive different digital competency trainings. Educational authorities can offer this training through synchronous, asynchronous, or a blend of both (Marchlik et al., 2021), called bichronous online learning (Martin et al., 2020), to accommodate teachers’ different needs.

Synchronous online learning

According to Martin et al. (2020), in synchronous online learning, students can participate in an online course from anywhere and receive most of the content online. Online meetings are held in real time, and students can log in from anywhere (Cheung, 2021; Kessler et al., 2021). Also, real-time interaction between teachers and learners is possible (González‐Lloret, 2020; Moorhouse & Wong, 2022). It has many affordances, such as a high rate of interactions, more engagement in group activities, response instantly to student concerns, and support (González‐Lloret, 2020; Wang & Zou, 2021). Synchronous online learning offers immediate feedback and provides audio-visual communication, which increases motivation (Utomo & Ahsanah, 2022). Teachers’ self-directed learning process could also be positively enhanced with synchronous online learning (Ironsi, 2022; Moorhouse & Kohnke, 2021a). Empirical evidence proved that including synchronous online learning can improve learning outcomes (Farros et al., 2020; Perveen, 2016), decrease attrition (Fowler, 2019) and lead to positive learners’ attitudes (Peterson et al., 2018). Lee et al. (2022) investigated how synchronous online learning influences teachers’ engagement, self-directed learning, and satisfaction in a Korean context. They liked synchronous online learning for their ability to engage in collaborative activities through Zoom breakout sessions. Nevertheless, this modality has some limitations, like scheduling conflicts, access to the internet and computer at specific times, technical issues, and discussions being too fast (Wang & Zou, 2021). Farros et al. (2020) claimed that synchronous discussion generally involves more effort and resources on the instructor’s part, and if students fail to learn, an asynchronous approach may be preferable.

Asynchronous online learning

According to Martin et al. (2020), asynchronous online learning is an online course that allows students to participate from anywhere at any time, with most of the content delivered online. In this modality, online meetings do not take place in real time. It provides access, self-pacing learning, and no scheduling conflict (Utomo & Ahsanah, 2022). Asynchronous online learning allows teachers to monitor work progress several times daily and continuously interact with peers. Hence, teachers feel part of a collective inquiry (Ge & Huang, 2022). Another appreciated feature is the possibility of collectively monitoring the gradually constructed product. In this modality, writing is dominant over speaking. This feature stimulates reflective skills and fosters the cognitive domain (Fowler, 2019). Alongside these contributions, differing participation levels, low collaboration, late responses, long waits to have the consent of all, unequal subdivision of work, and missing direct contact are assumed to pose threats to reap its advantages (Utomo & Ahsanah, 2022). Educational authorities should consider leveraging both the benefits of synchronous and asynchronous online learning (Brzezinska, 2022; Guillén et al., 2020; Moorhouse & Wong, 2022).

Bichronous online learning

Martin et al. (2020) referred to the blend of synchronous and asynchronous online learning as bichronous, grounded in cornification in time. It is defined as a blending of both asynchronous and synchronous online learning (see Fig. 1), where students participate in anytime, anywhere learning during the asynchronous portions of the course while participating in real-time activities during the synchronous modality (Martin et al., 2020, 2023). In bichronous online learning, self-pacing, immediate feedback, interaction, and audio-visual communication are available. Empirical evidence has supported the inclusion of synchronous elements in an asynchronous course (Brzezinska, 2022; Knowles, 2022; Peterson et al., 2018). In a mixed-method study, Moorhouse and Wong (2022) found that teachers accessed a variety of asynchronous and synchronous modalities to facilitate students’ learning, assess learning, and communicate with their students. Also, Utomo and Ahsanah (2022) explored the challenges associated with higher education in Indonesia and how Indonesian students perceived bichronous online learning. There was a positive perception of bichronous online learning among students regarding motivation, academic achievement, communication, and interaction. As a result of bichronous online learning, students were engaged, actively interacted with, and exchanged feedback, which influenced their learning outcomes significantly. Also, Brzezinska (2022) found that teachers need encouragement to get additional training and qualifications. There needs to be an online community to provide support. In addition, she found teachers should be informed of rationale justification and clarification as to why and how to use bichronous online learning. For instance, bichronous online learning is a suitable learning environment for implementing PBL (Coiado et al., 2020). Bichronous online learning supports BPL through modeling, scaffolding, feedback, and collaboration (Ge & Huang, 2022). Furthermore, synchronous online learning increases the sense of social presence (Lajoie et al., 2020), while asynchronous online learning allows for deeper and more thoughtful communication (Martin et al., 2023) in implementing PBL.

Fig. 1
figure 1

Conceptual Model of Bichronous Online Learning (Martin et al., 2020)

Project-oriented CALL professional development

PBL is primarily informed by cognitive and social learning theory (Weber et al., 2018) and is believed to promote more profound and meaningful learning through knowledge construction (Al-Busaidi & Al-Seyabi, 2021). PBL refers to a method of teaching and learning in which learners develop knowledge through designing, developing, and completing projects (Choi et al., 2019). PBL involves teachers working together to solve a problem and develop a product through self-directed inquiry, self-planning, and investigating (Kong et al., 2022). This approach actively engages learners in inquiry and emphasizes the importance of authentic, real-world activities for independent thinking and autonomous learning (Tsybulsky et al., 2020). PBL promotes deep and active learning by placing teachers in a situated learning context in which problem-solving, reflection, and interaction are encouraged (Powell & Bodur, 2019; Teräs, 2016; Tseng & Yeh, 2019).

Researchers proved the affordances of PBL in teacher professional development courses (Al-Busaidi & Al-Seyabi, 2021; Ge & Huang, 2022). According to Lee and Blanchard (2019), teachers who used PBL and experienced more formal PBL professional development were perceived as more competent and rated this pedagogy higher than those who did not experience it. They claimed that formal PBL professional development is crucial for increasing teachers’ intent to implement PBL. Also, Tseng and Yeh (2019) tried to improve teachers’ CALL competency through an 18-week project. Data revealed that teachers showed higher CALL competency after the PBL implementation. Hence, qualitative data demonstrated the benefits and the obstacles they faced in PBL. Furthermore, Nami (2022) conducted a qualitative case study on how PBL could contribute to CALL pedagogical knowledge. Drawing on the data obtained, PBL enhanced teachers’ technological knowledge and fostered teachers’ understanding of the constraints, selection, implementation, and assessment of technological tools.

Methods

Research design

An exploratory qualitative case study examined how synchronous, asynchronous, and bichronous online learning could foster teachers’ CALL pedagogical knowledge through BPL. The case study provides the chance to explore the detailed analysis in a real and meaningful context (Crowe et al., 2011). This approach was selected to focus on the case of thirty Iranian EFL teachers and aimed to explore the improvement in teachers’ CALL pedagogical knowledge. The researcher contacted the volunteers via email and asked about the type of modality that suited their schedule (synchronous, asynchronous, or bichronous). All participants were assigned to their convenient delivery modes with one weekly session that continued for six weeks. Hence, the participants attended a CALL professional development course and were divided into three groups: synchronous, asynchronous, and bichronous online learning. The three groups received instructions, developed a project collaboratively, and shared it with the class for further discussion. In synchronous group, instructions, project sharing, and classroom discussions happened online in real-time audio and video conferencing sessions. In asynchronous group, teachers received instructions offline through pre-recorded videos. Participants uploaded audio-narrated technology-review projects and experienced asynchronous discussions. Also, the bichronous group received online instructions, followed by asynchronous project sharing and discussions.

Participants and research context

A total of thirty English language teachers from different language institutes and high schools in Shiraz, which is located in southwest Iran, participated. The age range of participants was from 26 to 48 who voluntarily signed up for a free CALL professional development course. The volunteer sampling procedure was followed through advertising and requesting teachers to volunteer to participate in the study. To specify their CALL pedagogical knowledge, teachers were required to complete a self-evaluation questionnaire developed by Tafazoli et al. (2020). Despite having extensive teaching experience ranging from three to fourteen years, most participants considered themselves novice or average technology users. There was no prior CALL-related professional development experience or knowledge of any pedagogical use of technology among teachers. Most teachers were MA or BA holders in teaching the English language, with one Ph.D. candidate (see Table 1). Participants’ anonymity was protected using pseudonyms. The researcher was the instructor and facilitator in this study.

Table 1 Demographic Data of Participants

Procedures

CALL professional development course

The researcher implemented synchronous online learning through WizIQ educational platform’s live session feature. WizIQ provides a user-friendly interface for teachers with limited CALL competency. Moreover, it offers free functionality for virtual classrooms and learning management systems. For the asynchronous group, the researcher uploaded the recorded videos into the e-learning cloud storage of WizIQ. Hence, the participants could have access to instructions anytime and anywhere. Also, due to the limitation of WizIQ, asynchronous project sharing and discussions were implemented through a WhatsApp group. The bichronous group received online instructions through WizIQ and did project sharing and discussions in a WhatsApp group. Communication was mainly via audio and text. The course provided systematic instruction, inquiry-oriented projects, and follow-up discussions to foster teachers’ CALL pedagogical knowledge. One of the course’s main objectives was to make teachers aware of the affordances and constraints of technological tools and understand when and how to integrate them into language instruction. Participants received the syllabus via email upon registration.

The first session was devoted to course specifications and an introduction to learning goals. Teachers read syllabus topics before each session, focusing on CALL’s conceptual foundations. Two categories of digital technologies have been introduced. First, there were tools and environments suited for creating text, audio, and video content (Podcasts, blogs, video editing technology, digital storytelling and presentation tools, wikis, assessment tools, and animation). The second group involved educational technologies for language learning (games, websites, EFL Web Quests). In synchronous group, minimum half of each class session was devoted to systematic instruction and discussions on the assigned topics. The remainder of the session was dedicated to technology use and related projects. But in asynchronous and bichronous groups, there were no time constraints for discussions after project sharing. The researcher asked questions encouraging teacher reflection and discussion, such as “What do you think?” “Why do you agree?” “Do you use it in your teaching context?” “Would you please elaborate more?” Discussions were intended to engage teachers in sharing experiences, problem-posing, and collaborative problem-solving. The exploratory and inquiry-based nature of these experiences were expected to enhance teachers’ understanding of different technologies.

Projects

The course aimed to develop CALL pedagogical knowledge for language instruction, and engagement in projects and follow-up discussions was essential. For this purpose, the researcher assigned technology-use and technology-review projects to this course to place teachers in a meaningful learning context to assess how various technological tools are used and evaluated. Teachers were required to use the technological tools listed in group one of the syllabus before each lesson since session two. The technology-use project was assigned to develop teachers’ technological proficiency (see Fig. 2). Furthermore, it was presumed that the experience would create positive perceptions and increase the likelihood that they would integrate technology into the classrooms. Also, it enabled teachers to develop digital instructional content for their classrooms. In each session, teachers discussed how they used technological tools and what problems might arise in using these tools since collaborative exchanges play a significant role in PBL. The purpose of these discussions was to invite further reflection on CALL pedagogical knowledge and do projects through collaborative problem-solving. To do the technology-review projects, teachers in groups of two ought to complete projects. Each group had to choose a technological tool related to group 2 tools and review their educational affordances in an audio-narrated format. Teachers reflected on their peers’ reviews through the project sharing process. Discussions on review projects followed the classroom meetings. According to Lin (2015), this process engaged teachers to interact with technology, instructional content, and peer collaboration.

Fig. 2
figure 2

Screenshots of Technology-reviews from Four Participants

Data collection

This study collected data from participants’ audio-narrated technology-review projects from synchronous, asynchronous, and bichronous groups. Furthermore, follow-up discussions were mainly through audio in the synchronous group and text in the asynchronous and bichronous groups, which were recorded and analyzed.

Data analysis

The researcher transcribed the contents of the audio-narrated projects and follow-up discussions. The researcher used a qualitative content analysis strategy to make reliable inferences from the transcripts. The content analysis process involves identifying and independently analyzing meaningful categories from each data source using a codification process (Blair, 2015). Coding was conducted based on prior codes, in which previously established codes were applied to the data. According to Ertmer and Ottenbreit-Leftwich (2010) and Hubbard and Levy’s (2006) conceptualization of CALL pedagogical knowledge, a prior coding strategy was applied. The researcher followed some procedures to ensure the reliability and trustworthiness of the coding and to protect the data from projection. First, inspired by Wood et al. (2005), to ensure thematic units related to each code, a framework with labels, definitions, and instances developed by Nami (2022) was followed as a reference (see Table 2). The framework included narratives that reflected teachers’ knowledge/understanding of (1) technology, (2) CALL affordances, (3) CALL constraints, (4) CALL materials development, (5) CALL materials selection, and (6) CALL evaluation. Following this, the researcher read the data via two rounds to identify narratives directly relevant to the initially established codes. The units of analysis varied from a single sentence to a paragraph or the entire message since, in some cases, text chunks larger than a sentence presented ideas (often intertwined) and were associated with a priori codes. Thematic units were counted as a single unit when they addressed similar codes. For units that addressed more than one code, multiple coding was applied. After one month, the coding process was repeated, and the coded units were compared. The Cronbach’s alpha reliability was 0.82 for class discussions and 0.95 for technology-review projects. For each category of thematic units, descriptive statistics (frequency and percentages) were calculated (Creswell & Poth, 2016; Koc et al., 2009; Mohammadi & Tafazoli, 2022), which are presented in Table 3. See Fig. 3 for the procedures followed in this study.

Table 2 Priori Codes and Their Descriptions (Inspired by Nami, 2022)
Table 3 Distribution of the Thematic Units Identified in Synchronous, Asynchronous, and Bichronous Online Learning
Fig. 3
figure 3

Schematic Design of Research Procedures, Data Collection, and Data Analysis

Findings

The findings derived from audio-narrated technology-review projects and follow-up discussions from synchronous, asynchronous, and bichronous groups are discussed here. Table 3 shows the frequency and percentage of each thematic unit distributed in three separate synchronous, asynchronous, and bichronous groups.

Synchronous online learning

There were 173 thematic units identified in the synchronous modality, of which 20.6% of instances were on technological knowledge, such as creating accounts on different platforms, 22.0% were related to affordances for CALL, and 24.9% were related to constraints for CALL. Also, 13.9%, 6.9%, and 5.8% were related to CALL material selection, CALL material development, and CALL evaluation, respectively (see Table 3).

Tara, who attended synchronous online learning, addressed the application of online learning platforms for audio recordings to improve students’ listening and speaking skills: “Students can create and share podcasts through the use of Alitu to improve their speaking and listening simultaneously” (affordances for CALL). She highlighted the technical aspects of such tools and platforms. She echoed, “Furthermore, Alitu will automatically transcribe your episodes, making your podcast more accessible to everyone; edit playback speed is one of my favorite features. Recording an hour-long call means you can listen back through it to make any edits half the time. With Alitu, you can do everything: record, edit, transcribe, and publish” (technological knowledge). Zara also noted, “English Level Checker is a simple Android app that provides a quick way to find out which level of English a user has, such as a beginner, elementary, pre-intermediate, intermediate, upper-intermediate, advanced, and near-native” (affordances for CALL).

Also, the following thematic units reflected teachers’ understanding of the demerits of online tools and platforms. Arash noted that “Duolingo does not support the Persian language, so it doesn’t help my students” (constraints for CALL). Kiana highlighted that “Babbel develops conversational skills that are applicable and useful. It is one of the highest-ranked programs that doesn’t grow with you after the basics are taught. The app only supports a limited number of languages, considering its age. For intermediates or advanced learners, there isn’t much to choose from. Also, there isn’t enough variety in the format of exercises” (constraints for CALL).

Asynchronous online learning

There were 170 thematic units identified in the asynchronous modality, of which 25.9% and 21.8% of thematic units were found to address technological knowledge and affordances for CALL, respectively. Moreover, 28.2% were related to constraints for CALL. Regarding CALL material selection, development, and evaluation, 13.5%, 5.9%, and 4.7% instances were found, respectively. CALL material selection, development, and evaluation were the least frequent thematic units in synchronous and asynchronous modalities.

Hanna pointed to the affordances of vocabulary learning application and said, “There are two things that make Memrise so powerful: spaced repetition and mnemonics. Each word is reviewed according to a spaced repetition algorithm that calculates how many times it needs to be reviewed. When it is time for a review, the app will remind you” (technological knowledge). Also, Elli noted, “With HelloTalk, students can practice speaking and eliminate the stress associated with the real-time conversation(affordances for CALL). She also mentioned, “By marking your top conversations or messages, you will not lose your favorite phrases. Also, you will always know how to pronounce the messages you receive with the text-to-voice option” (technological knowledge).

Paria said, “With TripLingo, you can even call a real translator when you are truly lost for words with the inbuilt voice translator” (technological knowledge). Minoo also highlighted that “Listen and Speak provides a set of predefined templates of how to pronounce and understand words; this Android app helps language learners improve their foreign language learning” (affordances for CALL). Moreover, Arsam highlighted, “Busuu is one of the largest online communities for language learners. My favorite part of this community is the interaction and cooperation between the members. With photos and recordings by native speakers, it provides extensive vocabulary practice and audio-visual English learning materials” (affordances for CALL).

Bichronous online learning

In bichronous online learning, in total, 254 thematic units were detected, of which 23.2% addressed technological knowledge, 18.1% echoed affordances for CALL, 18.1% addressed constraints for CALL, and 15.7%, 13.4%, and 11.4% were related to CALL material selection, development, and evaluation, respectively. In bichronous online learning, more thematic units were found related to CALL material selection, development, and evaluation than synchronous or asynchronous modalities.

Omid showed Verb Trainer’s implication in creating grammatical material: “Integrate grammatical features and vocabularies and create your instructional text” (CALL material development). Samira mentioned, “With TexToys, you can create interactive language learning exercises for web pages. In addition to creating the exercises, you can deliver them to your students as web pages” (CALL material development).

Samin also shed light on the application of IELTS Speaking Assistant to choose content for speaking skills: “You can find good topics and ideas to improve students speaking and prepare them for international exams” (CALL materials selection). Also, Mari noted, “UVic’s Language Teaching Clipart Library contains approximately 3000 images that will help teach basic vocabulary. In addition to providing a set of basic graphics that are useful for low-level language teaching, it makes them as searchable as possible. This is ideal for beginners. It provides pictures to define words” (CALL material selection).

Tina addressed the application of Socrative to create language tests. She echoed, “Create quizzes and tests for your students to complete, with instant feedback for them and a progress tracking tool for you” (CALL evaluation). Sina showed good knowledge of CALL evaluation; he highlighted, “You can create interactive multiple-choice, short answer, jumbled sentence, crossword, matching/ordering, and gap-fill exercises for the World Wide Web with the Hot Potatoes application. Freeware Hot Potatoes may be used for any purpose or project” (CALL evaluation). Moreover, Fariba highlighted that “On the teacher’s computer, Markin runs as a windows program. You can import a student’s text for marking using the clipboard or a document file. Markin provides a comprehensive set of tools for marking and annotating texts after they have been imported. The teacher’s marks and annotations appear as colored text in the document after Markin has completed marking. The student can click on the marks to reveal more details about what the teacher has written or annotated in this document” (CALL evaluation).

Discussion

The study revealed the potential of synchronous, asynchronous, and bichronous online learning to foster teachers’ CALL pedagogical knowledge through PBL. In this study, teachers’ CALL pedagogical knowledge did not improve equally in synchronous, asynchronous, and bichronous online learning. Online delivery modes seem to affect how teachers improve CALL pedagogical knowledge. Regarding CALL material selection, development, and evaluation, fewer instances were found in synchronous and asynchronous online learning compared with bichronous online learning. The majority of instances demonstrate the superiority of bichronous online learning to synchronous or asynchronous modalities.

It might be due to the different features of each modality. Regarding the findings, it is assumed that participants are subject to different types and frequencies of interactions in each modality. According to researchers, although synchronous online learning provided learners with immediate feedback (Mohammadi & Tafazoli, 2022), instructor availability (Lee et al., 2022), and a sense of community (Cong, 2020), the participants gained less than bichronous online learning. The reason might be connectivity issues, which corroborates the findings of Knowles (2022), the tedium of being online at a particular time, an issue that was reported by Pulham and Graham (2018) and Perveen (2016). This study confirmed Fadhilah et al. (2021), who found synchronous online learning has more affordances than asynchronous online learning.

The participants’ inadequate success in asynchronous online learning might stem from the instructor’s lack of social and teaching presence, which corroborates the findings of Gunes (2019) and Knowles (2022). Participants may also suffer from isolation as a drawback of asynchronous online learning since they cannot meet their classmates (Knowles, 2022). The lack of spontaneity and visual cues and the time it takes for discussions and feedback to develop can frustrate participants, an issue confirmed by Martin et al. (2023). Also, regular checking in and monitoring of discussions requires self-directedness and discipline on the part of participants, which might be the constraint of asynchronous online learning, highlighted by Lowenthal et al. (2017). Also, asynchronous online learning may limit the opportunities for real-time interaction (Lo et al., 2021; Marshall & Kostka, 2020) and regular communication between students and teachers. These findings are in line with Alblooshi (2021) and Knowles (2022), who found that asynchronous online learning was the least preferred mode among the participant due to the lack of support and the inability to get help.

There seems to be a lack of efficacy in providing effective instruction solely through asynchronous or synchronous modalities. The findings suggest using bichronous online learning to combine the strengths of both synchronous and asynchronous modalities and address each other’s deficiencies. In bichronous online learning, by blending synchronous and asynchronous modalities, the researcher  could potentially overcome some of the shortcomings of asynchronous online learning alone, including the lack of immediacy, community, interaction, and audio-visual communication.

This study suggests that synchronous and asynchronous modalities must be combined to increase teachers’ CALL pedagogical knowledge. The complementary nature of synchronous and asynchronous online learning may have contributed to the success of bichronous online learning. Researchers provided similar results in different studies (Brzezinska, 2022; Islam, 2019; Moorhouse & Wong, 2022). This study, as opposed to similar studies, explored the efficacy of different modalities after teachers experienced synchronous, asynchronous, and bichronous online learning. In bichronous online learning, the instructor used synchronous and asynchronous modalities depending on their affordances. Teachers’ success in bichronous online learning might stem from assessing, offering feedback, and providing real-time interaction and asynchronous reflection, which corroborates the study by Alblooshi (2021) and Mohammadi (2022). Different affordances of bichronous online learning like positive perception (Utomo & Ahsanah, 2022), develop collaboration (Riwayatiningsih & Sulistyani, 2020), and learning flexibility (Alblooshi, 2021) might have led to fostering teachers’ CALL pedagogical knowledge. Thus the success of bichronous online learning might be due to its self-pacing nature and live teacher guidance which supports the findings of Knowles (2022). Bichronous online learning provides active participation in a flexible learning environment where passive learning is impossible. Teachers might sometimes feel a greater sense of connection through bichronous online learning, which strengthens social presence. Through bichronous online learning, teachers were engaged, actively interacted with, and exchanged feedback, contributing to their learning outcomes. This study provides evidence that bichronous online learning can strengthen the principles of the Community of Inquiry model (Garrison et al., 2010), which emphasizes that teaching, cognitive, and social presence are essential aspects of online course design and facilitation. While there is a high level of cognitive presence through reflection in asynchronous online learning, synchronous online learning is assumed to develop social presence through a higher chance of interaction and rapport (Brzezinska & Cromarty, 2022). Brzezinska’s (2022) study indicated that social and teaching presence significantly predicts cognitive presence, and most cognitive presence is determined by social presence. Furthermore, integrating PBL into bichronous online learning is an ideal learning setting to aid the acquisition of 21st-century skills (Brzezinska, 2022; Chai & Kong, 2017). This study confirmed that doing PBL in Bichronous online learning provides an ideal condition to foster critical thinking, problem-solving skills, self-directed learning, communication, and collaboration, which are the essential components of 21st-century skills (Chai & Kong, 2017).

Conclusions and implications

This study sought to foster teachers’ CALL pedagogical knowledge in synchronous, asynchronous, and bichronous online learning through PBL. The findings showed that bichronous online learning was more effective in enhancing CALL pedagogical knowledge than synchronous or asynchronous modalities. The reason was that bichronous online learning benefited from blending the best affordances of synchronous and asynchronous modalities. The study showed that synchronous and asynchronous online learning are complementary and should not be substituted. Hence, through implementing CALL teacher education programs in bichronous online learning, teachers may gain adequate technical, pedagogical, and content knowledge (Martin et al., 2023). These findings have several implications. The study examined and validated a pathway for developing teachers’ CALL pedagogical knowledge in a bichronous online modality through PBL, an essential step to moving away from ERT (Tafazoli, 2021). Also, according to Kong et al. (2017), new emphasis has been placed on using different online modalities to equip teachers with 21st-century skills with the evolution of online teaching. Hence, this study recommends setting up teacher professional development programs in bichronous online learning and preparing frontline teachers for a comprehensive mastery of technological operations concerning online teaching.

Limitations and future research directions

Even though the study yielded valuable findings, its scope and method have limitations. The scope of this case study was limited in time. There is a need for further research on evaluating OTPD over a more extended period. Also, it would be beneficial to conduct a more extensive study examining the impact of OTPD on teachers from various contexts. Furthermore, it would be helpful to use different research methods. Qualitative approaches are appropriate for an initial investigation in an emerging field; however, a mixed-method study that combines quantitative and qualitative methodologies would likely yield more robust results.