This paper investigates the relationship between stream placement and the academic progress made by children in England in Year 2 of primary school, drawing on data from the longitudinal Millennium Cohort Study (MCS). The MCS is a sample of 19,000 children born across the UK around the turn of the century and their families. Academic progress was compared between children in England in the "top", "middle" or "bottom" streams, and among the majority of non-streamed children. Multiple regressions took into account child, family and school characteristics and showed that stream placement significantly impacted on the academic progress made by children. Children in the "top" stream achieved more and made significantly more academic progress than children attending schools that did not stream, while children in the "middle" or "bottom" streams achieved less and made significantly less academic progress. The reasons for this and the educational implications are discussed.