This study investigates which aspects of teaching quality (TQ) are related to progress in student learning outcomes and whether students have equal access to high-quality instruction. Evidence identifies TQ as a fundamental driver of student learning and a critical link to educational equity (e.g. Fauth et al., 2021; Darling-Hammond, 2000). However, it remains unclear which specific TQ dimensions matter most for learning progress, as findings vary across countries and cohorts (Blömeke et al., 2019). These inconsistencies are often attributed to varying conceptualizations of TQ and methodological limitations (Klieme & Nilsen, 2022). While qualitative studies offer deep insights, they lack generalizability. Conversely, quantitative research frequently relies on cross-sectional designs prone to omitted variable bias and reversed causality, hindering robust causal inferences. Consequently, there is an urgent need for longitudinal research using representative samples and validated frameworks that allow for comparisons across countries and cohorts. This study addresses these gaps by utilizing the complete longitudinal dataset from the TIMSS Longitudinal project and adopting the Three Basic Dimensions framework (Klieme et al., 2009). This framework, comprising classroom management, supportive climate, and cognitive activation, provides a validated, standardized basis for comparison (Praetorius et al., 2018; Klieme & Nilsen, 2022). The analysis encompasses all participating countries across both available cohorts: a primary cohort (Grade 4 to 5) across nine countries, and a lower secondary cohort (Grade 8 to 9) across three of these countries. Using two-level regression analyses (students nested within classes), the study investigates the impact of the three TQ dimensions on mathematics achievement gain. Additionally, it examines the relationship between student socioeconomic status and TQ to determine if high-quality teaching is equitably distributed. Missing data will be handled using robust maximum likelihood (RML) estimation to ensure the integrity of the longitudinal findings. The data will be available in February 2026. Based on previous research (e.g. Praetorius et al., 2018; Klieme & Nilsen, 2022), we hypothesize that classroom management and cognitive activation will demonstrate stronger impacts on cognitive outcomes than supportive climate. We further hypothesize that the equitable distribution of high-quality teaching will vary according to the broader educational equity profiles of the participating countries. These findings will contribute to the global debate regarding the role of teaching quality in fostering both academic excellence and social equality.

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