The prevalence of 'pre-service' or 'trainee' teachers in schools is rising in England, driven by the expansion of school-led routes to qualified teacher status and increasing demand for newly qualified teachers. This may have important implications for schools, which have historically been concerned with the impact of trainee teachers on their pupils' attainment. There are, however, confounding factors which affect both the decision to host a trainee teacher and pupil attainment. We empirically model the impact of trainee teachers on contemporaneous pupil attainment in 'high-stakes' exams, exploiting unique data combining national administrative data on pupil test scores with a survey of schools' involvement with initial teacher training over multiple academic years. We use school fixed effects to account for time-invariant school factors which may determine both schools' teacher training decisions and pupil attainment. Counter to schools' concerns, we find that pupil attainment in high-stakes assessments, on average, is not significantly affected by the number of trainee teachers. This is an important empirical finding, as it suggests that the rapid expansion of school-led teacher training is not likely to have a detrimental effect on pupil attainment in England, conditional on the set of schools that choose to engage with initial teacher training remaining similar: trainee teachers may still affect pupil attainment in schools that do not currently participate in initial teacher training, as these schools are typically more constrained.