We consider the effect of teaching practices on the persistence of school-entry age effects caused by rigid cutoff dates for school eligibility in Spain. We document significant school-entry age effects for the same cohort of students when they were in elementary and secondary school. Then, we test whether school-entry age effects at age 15 are lower for those students who were more frequently exposed in elementary school to modern teaching practices, grounded in active and cooperative learning. We find that the relationship between teaching practices and age effects is non-linear. Extreme bias toward any practice, modern or traditional, by elementary teachers exacerbates age effects. Conversely, age effects are mitigated when elementary teachers follow a balanced approach that combines different teaching styles.