The study reported in this article investigated the differential effects of teachers on female, minority, and low-socioeconomic-status (SES) students' achievement. I used data from a 4-year, large-scale, randomized experiment (Project STAR) that was conducted between 1985 and 1989 in Tennessee, in which students and teachers were randomly assigned to classrooms within schools. The sample consisted of nearly 11,000 elementary students in 79 schools who participated in the experiment from kindergarten through third grade. Data from Project STAR included information about student outcomes such as Stanford Achievement Test scores in mathematics and reading and student demographics such as gender, race, and SES. I used multilevel models to examine how teacher effects interacted with student gender, race/ethnicity, and SES. Similar methods were employed to explore whether teacher effects were more pronounced in high-poverty schools. Teacher effects were measured as residual variability in achievement among classrooms within schools. Results indicated that all students benefited from effective teachers. The differential teacher effects on gender, race, and SES were overall small and insignificant. However, there was some weak evidence that females, whites, and high-SES students might benefit more from teacher effects than other students. In addition, there was some, although mixed, evidence that teacher effects were more pronounced in lower-SES schools. (Contains 9 tables.)