We exploit within-teacher variation in the years that teachers host an apprentice ("student teacher") in Washington State to estimate the causal effect of these apprenticeships on student achievement, both during the apprenticeship and afterwards. The average causal effect of hosting a student teacher on student performance in the year of the apprenticeship is precisely estimated and indistinguishable from zero in both math and reading, though effects are large and negative in math when ineffective teachers host an apprentice. Hosting a student teacher is also found to have modest positive impacts on student math and reading achievement in a teacher's classroom in following years.