Learning that Lasts: Unpacking Variation in Teachers’ Effects on Students’ Long-Term Knowledge

Measures of teachers’ “value added” to student achievement play an increasingly central role in k-12 teacher policy and practice, in part because they have been shown to predict teachers’ long-term impacts on students’ life outcomes. However, little research has examined variation in the long-term effects of teachers with similar value-added performance. In this study, we investigate variation in the persistence of teachers’ value-added effects on student achievement in New York City. We separate persistent effects into general effects that improve both the subject taught (math or English language arts (ELA)) and the other area of measured achievement and subject-specific effects which improve only the subject taught. Two findings emerge. First, a teacher’s value-added to ELA achievement has substantial crossover effects on long-term math performance. That is, having a better ELA teacher affects both math and ELA performance in a future year. Conversely, math teachers have only minimal long-term effects on ELA performance; their effects are far more subject-specific. Second, we identify substantial heterogeneity in the persistence of English Language Arts (ELA) teachers’ effects across observable student, teacher, and school characteristics. In particular, teachers in schools serving more poor, minority, and previously low-scoring students have less persistence than other teachers with the same value-added scores. Moreover, ELA teachers with stronger academic backgrounds have more persistent effects on student achievement, as do schools staffed with a higher proportion of such teachers. The results indicate that teachers’ effects on students’ long-term skills can vary as a function of instructional content and quality in ways that are not fully captured by value-added measures of teacher effectiveness.