We use a novel database of student teaching placements in Washington State to investigate teachers' transitions from student teaching classrooms to first job classrooms and the implications for student achievement. We find that first-year teachers are more effective when they are teaching in the same grade, in the same school level, or in a classroom with student demographics similar to their student teaching classroom. We also document that only 27% of first-year teachers are teaching the same grade they student taught, and that first-year teachers tend to begin their careers in higher-poverty classrooms than their student teaching placements. This suggests that better aligning student teacher placements with first-year teacher hiring could be a policy lever for improving early-career teacher effectiveness.