School leaders are assumed to be important for the implementation of data-based decision making (DBDM), but little is known about changes in leadership during this implementation. Educational leadership was measured before, during, and after a two-year, school-wide DBDM intervention in 96 primary schools. Advanced analysis techniques were applied: educational leadership was classified based on multilevel latent class analysis, changes were modeled using multi-state modeling. Results indicate that leadership was stable (44%) or improved (40%) during DBDM implementation. Stability was primarily found for schools with initial high leadership for DBDM, whereas improvement was most likely in schools with lower initial leadership