Teamteaching has received much attention over the past two decades (Walsh, 2020). In this instructional strategy, two or more teachers work together in planning, implementing and/or evaluating a lesson or series of lessons (Baeten & Simons, 2014). Team teaching is considered an innovative strategy to enhance teaching and learning (Simons et al., 2020). While some research has been conducted on team teaching, limited studies have focused on (observed) teaching behaviour within this context (Vembye et al., 2023).

This mixed-method study fills this gap by integrating observational data with teachers' self-reported experiences based on questionnaires and team interviews. These data types complement each other and offer a more comprehensive understanding by combining objective observations with personal and contextual perspectives. Moreover, by examining the alignment between teachers' perceptions and observed behaviour, the study provides a nuanced understanding of the factors causing differences in teaching effectiveness.

More specifically, this study seeks to answer the following two research questions:

1. To what extent do teachers exhibit effective teaching behaviour during team teaching?
2. What factors influence teachers' effective teaching behaviour during team teaching?

Van de Grift's (2007) ICALT framework serves as a theoretical lens for studying effective teacher behaviour, which is defined as behaviour that positively influences student’s academic outcomes (van de Grift, 2007). The ICALT framework consists of six dimensions of effective teacher behaviour that have been shown to influence students' academic outcomes (van de Grift, 2014): (1) creating a safe and stimulating learning environment, (2) organising efficient classroom management, (3) providing clear and structured instruction, (4) delivering intensive and interactive lessons, (5) teaching learning strategies, and (6) adapting the lesson to teaching needs.

To answer the two research questions, a multiple case study design (Yin, 2014) is set up. More specifically, a mixed-method approach with an explanatory sequential design is used (Creswell & Plano-Clark, 2017). A convenience sampling method was employed, selecting readily available or easily accessible teacher teams. However, these teams needed to meet several criteria. Specifically, they were required to be (1) experienced teams that (2) regularly engaged in team teaching practices, and (3) implement team teaching before, during, and after lessons. Mainly, schools that had participated in previous research on team teaching were directly approached for participation. All teams participated voluntarily and all teachers provided their informed consent. Ultimately, twelve team teaching teams (with a total of 27 teachers) were selected: six from primary education and six from secondary education. Data were collected using three distinct methods: (1) video-based observations, (2) teacher surveys, and (3) team interviews. The data collection was carried out from April 2023 to January 2024. One full lesson (standard 50 minutes) per team was recorded. Surveys were administered to gather background information and teachers' self-perceptions of effective teaching. These surveys provided context and complemented the video observations. Team interviews were conducted to delve deeper into the factors influencing the success of team teaching. Through triangulation of these three data collection methods, the study aimed to achieve a comprehensive understanding of effective teaching behaviour during team teaching.

The results show that during team teaching, teachers show effective teaching behaviour in the less complex dimensions of teaching, such as creating a safe and stimulating learning climate, organising efficient classroom management and providing clear and structured instruction. In contrast, challenges arise in the more complex dimensions of effective teaching such as providing an intensive and activating lesson, incorporating differentiation and teaching learning strategies. Moreover, a striking finding is the discrepancy between observed teaching behaviour and self-reports: teachers often overestimate their effectiveness in the more complex dimensions. Interviews also point to four key elements that influence effective teaching behaviour: (1) collaboration, (2) role clarity and task assignment, (3) reflection and (4) infrastructure. For instance, teachers emphasize the importance of constant communication and a personal connection, a clear division of tasks to avoid misunderstandings, and regular (in)formal evaluations in which concrete situations can be discussed. In addition, the available infrastructure plays a determining role in the choices and possibilities within the teaching approach. The integration of multiple data sources provides valuable insights into the complexity of effective teaching behaviour during team teaching, with implications for theory, practice and policy. For theory, it contributes to a deeper understanding of the dynamics of team teaching and, more specifically, insights into effective teaching. For practice, these insights can help teachers design more effective team-teaching strategies, promoting better collaboration, role clarity and division of labour, and reflection among teachers. For policy, the findings can inform further professionalisation and encourage schools to provide adequate infrastructure.

Baeten, M., & Simons, M. (2014). Student teachers' team teaching: Models, effects, and conditions for implementation. Teaching and Teacher Education, 41, 92-110. https://doi.org/10.1016/j.tate.2014.03.010 Creswell, J., & Plano-Clark, V. (2017). Designing and conducting mixed methods research. Thousand Oaks, CA: Sage Publications. Simons, M., Coetzee, S., Baeten, M., & Schmulian, A. (2020). Measuring learners' perceptions on a team taught learning environment Development and validation of the LTTPQ. Learning Environments Research, 23, 45-58. https://doi.org/10.1007/s10984-019-09290-1 Van de Grift, W. (2007). Quality of Teaching in Four European countries: A Review of the Literature and Application of an Assessment Instrument. Educational Research, 49(2), 127-152. https://doi.org/10.1080/00131880701369651 Vembye, M., Weiss, F., & Hamilton Bhat, B. (2023). The Effects of Co-Teaching and Related Collaborative Models of Instruction on Student Achievement: A Systematic Review and Meta-Analysis. Review of Educational Research. https://doi.org/10.3102/00346543231186588 Walsh, T. (2020). ‘Promoted widely but not valued’: Teachers’ perceptions of team teaching as a form of professional development in post-primary schools in Ireland. Professional Development in Education, 48(4), 688-704. https://doi.org/10.1080/19415257.2020.1725596 Yin, R. (2014). Case study research: Design and methods (5th ed.). Thousand Oaks, CA: Sage Publications.