Based on teacher evaluations of principals instructional leadership from almost 2,000 Swedish schools between 2013 and 2021, the study shows that principals leadership improves pupils final grades partly by fostering teacher collaboration. For standardized test scores, however, teacher collaboration appears less important, with principals’ direct leadership playing a stronger role.

These effects are most visible as differences between schools, while achieving change within schools proved more difficult. An important conclusion is that to truly understand leadership in schools, we need to study principals and teachers together - as their interaction is key to understanding pupil achievement and overall school performance.