How Large Are Teacher Effects?

TLDR

Teacher effectiveness varies, but empirical evidence is weak and largely based on econometric studies that attempt to control for selection bias. The study estimates teacher effects on student achievement using data from a four‑year randomized experiment of teachers and students. Teacher effects were estimated as between‑teacher variance components of achievement status and residualized achievement gains within schools. Teacher effects on achievement gains are comparable to prior studies but larger for mathematics than reading; teacher experience relates substantially to gains, significant only for 2nd‑grade reading and 3rd‑grade math; and teacher effect variance is markedly higher in low‑SES schools than in high‑SES schools.

Abstract

It is widely accepted that teachers differ in their effectiveness, yet the empirical evidence regarding teacher effectiveness is weak. The existing evidence is mainly drawn from econometric studies that use covariates to attempt to control for selection effects that might bias results. We use data from a four-year experiment in which teachers and students were randomly assigned to classes to estimate teacher effects on student achievement. Teacher effects are estimated as between-teacher (but within-school) variance components of achievement status and residualized achievement gains. Our estimates of teacher effects on achievement gains are similar in magnitude to those of previous econometric studies, but we find larger effects on mathematics achievement than on reading achievement. The estimated relation of teacher experience with student achievement gains is substantial, but is statistically significant only for 2nd-grade reading and 3rd-grade mathematics achievement. We also find much larger teacher effect variance in low socioeconomic status (SES) schools than in high SES schools.