This contribution consolidates insights from the large-scale research project 'ESTAFETT', funded by the Research Foundation Flanders, on the effects of team teaching on both teachers and students. We focus on the relationship between team teaching, effective teaching behavior, and student outcomes. Team teaching refers to a practice where two or more teachers collaborate to a certain extent and share responsibility in the preparation, execution, and evaluation of a lesson or series of lessons (Baeten & Simons, 2014). In the project, various research methods were combined in four studies: a large questionnaire survey (with 479 respondents who are team teaching) (S1), multiple case studies with video observations (involving 27 teachers from 12 team teaching teams) (S2), an experimental study (with 267 students and 16 teachers participating) (S3), and an intervention study (with 16 starting team teaching teams) (S4). Teachers report more effective teaching with team teaching than with individual teaching, especially in differentiation and activating teaching methods, but the perceived added value depends on the education level (S1, S4). Next, we observed a significant amount of effective teaching behavior regarding creating a safe and stimulating learning environment, classroom management, and clear instructions. However, there is considerable variation within teams on more complex dimensions (S2, S4). Patterns of growth, stagnation, regression, fluctuation, or struggle are observed throughout the school year, particularly for the more complex dimensions of effective teaching behavior (S4) (Decuyper et al., 2024; De Weerdt et al., 2024; Mariën et al., 2023). Students see as main advantages increased support (S3, S4) and the variety of explanations (S4). We also observe slightly positive effects on academic outcomes (S4): students in team teaching settings achieve slightly better results than those taught by individual teachers, especially with fewer students per teacher. Additionally, team teaching has a positive effect on students' feelings of competence but does not significantly impact other non-cognitive outcomes (autonomy, belonging, and engagement) (S4) (De Weerdt et al., 2024). To conclude, team teaching can be considered as a goal-oriented form of collaboration that promotes quality education for all students. It provides opportunities to enhance teachers' effective teaching behavior, provided that a variety of models, roles, and grouping forms are employed, aligned with the goals and needs of both students and teachers. The school is responsible for ensuring the conditions necessary for a successful implementation: a clear vision on the goals of team teaching, school-wide support, regular consultation meetings, and practical conditions.

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