Collaboration among teachers has been internationally recognized as a central factor in promoting inclusive education (e.g., Paulsrud & Nilholm, 2023). More specifically, intensive collaboration is assumed to have the potential to support teaching practices and school development by integrating teachers’ different areas of expertise and fostering professional development, thereby enhancing outcomes for both teachers and students (e.g., Grosche et al., 2020; Pan et al., 2024).

Existing evidence suggests that collaboration can indeed positively affect student outcomes, such as their academic achievement or social participation (e.g., Ronfeldt et al., 2015; Spörer et al., 2021). At the same time, unintended and potentially negative effects, such as less peer interaction and more teacher interaction when a second teacher is in the classroom, must also be considered (e.g., Spörer et al., 2021). However, empirical evidence remains limited, particularly regarding longitudinal studies on teacher collaboration outside the classroom and the characteristics of collaboration that most effectively support student outcomes (e.g., Sannen et al., 2021).

This study aims to address this research gap by drawing on the theoretical framework of co-constructive collaboration (Grosche et al., 2020; Kluge et al., 2025), a model that is compatible with international concepts of teacher collaboration, such as professional learning communities (Grosche et al., 2020). Co-constructive collaboration (CCC) is defined as “joint, cyclical, intensive, and interdependent processes of negotiation and reflection [among teachers] on innovations and their practical implications” (Grosche et al., 2020, p. 467, translated by the authors). It represents an intensive form of classroom related or extra-curricular collaboration, which encompasses collaborative activities that occur before and after lessons (Kluge et al., 2025; Schnepel et al., 2025).

Grounded in this theoretical framework, the present longitudinal study examines whether different dimensions of CCC can improve students’ competencies in math and reading, their perception of inclusion(i.e., their academic self-concept, emotional well-being, and social inclusion; Venetz et al., 2015), as well as their development in these domains from grade six to grade nine.

By examining different dimensions of collaboration, the study provides insights into which characteristics of collaboration among teachers are most effective in promoting student outcomes. Furthermore, by integrating academic, emotional, and social outcomes of students, this study provides a comprehensive understanding of the potential role of teacher collaboration in promoting students’ development in inclusive lower secondary schools.

Data for this study was drawn from the research project “Inclusion in and after lower secondary schools” (INSIDE, Gresch et al., 2026). INSIDE is a longitudinal cohort study following two consecutive waves of students in Germany from lower secondary education to the transition into the labor market. For this study, we used the first three time points, collected between 2019–2023 in grade six, seven, and nine. 2,165 students (48 % female) in 164 schools were included in the analyses. A migration background was reported for 30 % of students (2 % missing information). 11 % of students were identified as having special educational needs (SEN). Across the participating schools, data on collaboration were available for at least one of the three time points for a total of 1,485 teachers (85 % general teachers and 15 % special education teachers). Student outcomes were assessed using the competence tests for reading and math from the National Educational Panel Study (NEPS, Stegenwallner-Schütz et al., 2022) as well as the internationally established Perception of Inclusion Questionnaire (PIQ), which measures how students perceive their academic self-concept, emotional well-being, and social inclusion (Venetz et al., 2015). The reliability of the variables was satisfactory in all cases (weighted likelihood estimates reliability in math and reading > 0.70, α > .75 for PIQ scales). CCC was assessed via teacher surveys using two questionnaires developed within the INSIDE project (Kluge et al., 2025). These questionnaires cover four dimensions of CCC: commitment to collaboration (e.g., shared understanding), co-constructive activities (e.g., negotiating shared goals), iterative revision as a specific co-constructive activity, and outcomes of co-constructive activities (e.g., shared responsibilities) (Kluge et al., 2025). All dimensions demonstrated good reliability (α ≥ 0.72). As both questionnaires demonstrated longitudinal measurement invariance and high reliability of the average of all items and time points (≥ 0.88 and ≤ 0.96), scale scores were aggregated across measurement points, providing stable and reliable estimates of different dimensions of CCC over time. To answer the research questions, latent growth models were estimated using Bayesian estimation for each of the five dependent variables, i.e., math and reading competence, academic self-concept, emotional well-being, and social inclusion. Both the intercept and slope were predicted by the CCC scales on the school level as well as by student control variables on the individual level (gender, migration background, and SEN). Missing values were handled via full information maximum likelihood.

Latent growth models showed acceptable to very good fit (BLTI = 0.955–0.999; BRMSEA = 0.031–0.133). For math, results indicated that a more intense iterative revision within CCC is associated with lower initial math competence (βrevision_intercept = -0.05), while a higher commitment to collaboration is associated with an increase in math competence (βcommitment_slope = 0.30). For reading as well as the academic self-concept, none of the different dimensions of collaboration showed a significant effect. For emotional well-being as well as social inclusion, a more intense iterative revision was associated with lower initial emotional well-being (βrevision_intercept = -0.18), whereas a stronger commitment to collaboration is associated with higher initial emotional well-being (βcommitment_intercept = 0.26). Furthermore, both dimensions of CCC also affected the development of social inclusion. While more intense iterative revision is associated with a greater decline of social inclusion over the three time points (βrevision_slope = 0.30), commitment mitigates the decline (βcommitment_slope = -0.42). Overall, collaboration appears to be more strongly associated with emotional and social aspects than with students’ academic and academic related outcomes. Moreover, the results show that not all dimensions of CCC are equally relevant, and that the dimensions that do matter can have both positive and negative effects on student outcomes. While teacher collaboration characterized by a shared understanding of work, and a common instructional approach among teachers (commitment), appears to be particularly important, intensive iterative revision of concepts and methods can have adverse effects on these domains as well as on students’ math competence. These and further findings will be discussed with reference to their implications for teacher collaboration in different educational contexts as well as for international research in this field. Furthermore, methodological (e.g., sample attrition) as well as conceptual limitations (e.g., the impact of the COVID-19 pandemic on students’ development) will be discussed.

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