Abstract
We study the effects of principal instructional leadership on pupil educational achievement using longitudinal data of 120,394 teacher responses across 1919 schools in Sweden over 9 years. Through multilevel structural equation modelling, we test how teacher ratings of principal leadership influence indicators of educational achievement and the extent to which this effect is channelled through a collaborative teacher culture in schools. Findings suggest that teacher collaboration partly mediates the relationship between principal instructional leadership and pupil educational achievement in terms of final year grade point average. However, concerning final year standardised test scores, principal instructional leadership alone has a stronger relationship to school performance than teacher collaboration. The longitudinal analysis suggests these patterns are driven by relatively stable differences between schools rather than dynamic changes in schools over time, indicating that variation in school contexts such as culture, organisational structure, and leadership practices persist over time. We discuss implications for research, practice, and policy on school leadership and teacher collaboration.