We use matched employee–employer records from the teacher labor market to explore the effects of late teacher hiring on student achievement. Hiring teachers after the school year starts reduces student achievement by 0.042 SD in mathematics and 0.026 SD in reading. This reflects, in part, a temporary disruption effect in the first year. In mathematics, but not in reading, late‐hired teachers remain persistently less effective, evidence of negative selection in the teacher labor market. Late hiring concentrates in schools that disproportionately serve disadvantaged student populations, contributing to challenges in ensuring an equitable distribution of educational resources for all students.