The 21^st century has yielded a time of rapid-paced change – socio-political and technological - and this has resulted in an even greater need for more effective teacher professional development (TPD) (Scott, 2010). TPD training has helped teachers formulate a personal and professional credo, develop an in-depth understanding of teaching-learning processes, and develop a sense of commitment to their role (Avidov-Ungar & Shamir-Inbal, 2017). The COVID-19 pandemic has had a major impact on students, parents, and teachers and it has forced changes into the educational process (Purwanto et al., 2020). The transition to remote learning during the COVID-19 pandemic posed many challenges, for which the education systems were not prepared, and required immediate and extensive support (Fauzi & Khusuma, 2020; Lockee, 2021). Moreover, the pandemic isolated teachers in their homes and has found them unprepared for the challenging tasks of online teaching, and lacking the professional skills to conduct online education (Avidov-Ungar et al., 2020; Trust et al., 2020).

One of the major issues that teachers faced was the lack of access to tailored and adapted TPD programs in order to assist them to deal immediately and successfully with ERT challenges (Sancar et al., 2021; Scott, 2010; Trikoilis & Papanastasiou, 2020). Researchers agree that online instructors need this TPD designed specifically for their teaching environment, largely because online teaching requires different skills than teaching in face-to-face or hybrid environments (Avidov-Ungar et al., 2020). To address the sharp transition to online learning, teachers spontaneously adopted a variety of informal ways, mainly through social media platforms to interact with colleagues in order to acquire the useful tools and skills for ERT (Holme, 2020; Lockee, 2021; Trust et al., 2020). In addition to informal peer learning, teachers were offered professional development processes through formal frameworks provided by the Ministry of Education (MoE, 2020).  Indeed, it has been found that formal or informal learning communities among teachers can act as powerful opportunities for teacher growth and development (Postholm, 2012).

TPD is a process that begins with a teacher education program and continues throughout a teacher’s professional life (Sancar et al., 2021). Studies examining teachers' careers discuss a "career cycle", which includes stages in teachers’ careers, from entering the profession until retirement (Furner & McCulla, 2019; Avidov-Ungar & Herscu, 2020). These studies have found three major teacher career stages: early - 1-7 years of seniority, middle - 8-23 years of seniority, and late-stage - 24+ years in teaching (Furner & McCulla, 2019; Avidov-Ungar & Herscu, 2020). Teachers in different career stages are characterized by different abilities and inclinations to learn new pedagogical approaches and by their willingness to incorporate classroom changes (Postholm, 2012).

In order to understand teachers’ learning and professional development that occurs in multiple online contexts, both formal and informal, this study examined the effectiveness and the contribution of such TPD processes during the first period of the COVID-19 pandemic (March-June 2020) compared with the second pandemic period (July-October 2020). The study considered teachers in different career stages, since the level of professional experience may affect the effectiveness of untraditional TPD.

The research questions were:

RQ1.   What are the characteristics of the online TPD of teachers in various career stages, in relation to informal-spontaneous and formal–institutional aspects, and their effectiveness, with a comparison between the two pandemic periods?

RQ2.  What is the contribution of online TPD to the techno-pedagogical knowledge of teachers in relation to their different career stages andin comparison to the two pandemic periods?

This mixed-method study is based on interviews with 60 elementary-school homeroom teachers in Israel. These teachers participated in online TPD during two periods of the COVID-19 pandemic: March-June 2020 (first period) and July-October 2020 (second period). The participating teachers were in various career stages - 20 teachers in each stage: early - 1-7 years of seniority, middle - 8-23 years of seniority, and the late-stage - 24+ years of teaching seniority. The study received approval from the Institutional Ethics Committee and from the Ministry of Education. Semi-structured interviews were conducted via the Zoom videoconferencing platform. During the interviews teachers were asked to address the following issues: 1. The type of informal-spontaneous and/or formal-institutional TPD learning they experienced throughout these two COVID periods. 2. The effectiveness of the informal and/or formal-institutional TPD learning. 3. The contribution of online TPD to the techno-pedagogical knowledge of the teachers. To ensure inter-rater reliability of coding teacher statements, 25% of the statements were analyzed by a second-rater, and the agreement level was high, Cohen's Kappa = .85. In addition, the Chi-Square goodness of fit test was conducted in order to define the significance of differences found in subcategories between the two pandemic periods and between the phases of the teachers' careers (1-7, 8-23, 24+ years). Participants' responses were mapped using bottom-up content analysis according to their different career stages and according to the two pandemic periods. Details of the categories are presented below. (1) Characteristics of online TPD -This category included two subcategories that addressed the TPD of teachers: informal-spontaneous and formal-institutional learning. (2) The contribution of online TPD - This category included a description of the teachers' techno-pedagogical knowledge that they had learned in the TPD. In these both aspects, Teachers' learning efficiency was analyzed according to the following specifications as low, moderate, and high, as described below. (1) Low- when training content did not help teachers implement digital learning. Sometimes the training created confusion, mainly because it was not suitable for the needs of the teachers. (2) Moderate - when the training only partially helped to deal with the situation. There were certain benefits, but at the same time, the TPD contained various limitations. (3) High - when training helped the teachers implement into practice what they had learned. The content learned was useful and contained a clear professional added value to the teachers.

The first research question yielded 1,344 (72%) statements). Teachers reported that during the pandemic two types of TPD took place: informal-spontaneous (n = 551), based mainly on self-directed learning and peer learning, and formal-institution TPD (n = 456), which included internal school initiatives, training at external teacher centers, or training organized by the MoE. Without appropriate formal TPD, teachers, especially those in the middle and senior career stages, turned to colleagues and to social media in order to cope with online instruction. The effectiveness of formal-institutional training (n = 215) was classified as significantly higher than the efficiency of informal spontaneous learning (n = 122), However, the effectiveness of informal training was reported as significantly higher during the second period compared to the first period. The second research question revealed six aspects of the contribution of TPD training (529 [28%] statements). Teachers, especially those in their late seniority careers, reported various digital tools they learned during their TPD (n = 262). These tools, which were learned significantly more during the second COVID period, improved both teaching and assessment. The second subcategory addressed the mastery and knowledge of the technology applications (n = 150) that reflected the use of technology for teaching in a more focused and creative way. Other contribution aspects were problem-solving skills (n = 37), especially for middle career teachers, and teachers felt that they could manage the online learning environment (n = 35), mainly in the second period. However, little attention was provided to students’ emotional needs (n = 29) and to the contribution of tailored assessment methods (n = 16). This study recommends (a) adapting formal institutional TPD to promote optimal pedagogical processes, and (b) strengthening peer learning and learning community skills. (c) TPD needs to be adapted to the specific characteristics of teachers in their certain career stages.

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