Results from experimental and nonexperimental studies have shown that teachers differ in their effectiveness. In addition, evidence from nonexperimental studies has indicated that teacher effects last for 3 years in elementary grades. This study uses data from Project STAR and its follow-up study, the Lasting Benefits Study, to examine whether teacher effects from kindergarten to fifth grade can simultaneously affect sixth grade achievement. Teacher effects are defined as teacher-specific residuals adjusted for student background and treatment effects. Findings indicate that the teacher effects persist through sixth grade in mathematics, reading, and science. The findings also suggest that teacher effects are important and that their cumulative effects on student achievement are considerable. (Contains 8 tables.)