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 first-year teachers are more effective when they teach in the same or an adjacent grade, in the same school type, or in a classroom with student demographics similar to their student teaching classroom. We 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.