The belief that children thrive if educated amongst higher-achieving schoolmates guides many parents in their choice of school. We extend the literature on this issue by considering children making the transition from primary to secondary schooling at age-11 in England. We use year-to-year changes in school composition to identify the impact of schoolmates on pupil progress at age 14. Traditional "linear-in-means" specifications lead us to conclude that prior achievements of a child's schoolmates are, on average, unrelated to his/her academic progress. However, this masks evidence that lower achieving pupils are disadvantaged by higher achieving schoolmates, whereas upper-middle ranking pupils benefit.