The authors examined the differential effects of teachers on female, minority, and low-socioeconomic status (SES) students' achievement in Grade 4. They used data from a randomized experiment (Project STAR) and its follow-up study (LBS). Student outcomes included Grade 4 SAT scores in mathematics, reading, and science and student demographics included gender, race, and SES. The authors used multilevel models to determine how teacher effectiveness interacted with student gender, race, and SES. We also explored whether teacher effects were more pronounced in schools with high proportions of minority or female students. Results indicated that all students benefited from having effective teachers. The differential teacher effects on female, minority, and low-SES students' achievement, however, were insignificant. There is some evidence in mathematics that teacher effects are more pronounced in high-minority schools. Finally, teacher effects seem to be consistent within and between schools. (Contains 8 tables.)