In 2000–2002 an innovative early years curriculum, the Enriched Curriculum (EC), was introduced into 120 volunteer schools across Northern Ireland, replacing a traditional curriculum similar to others across the UK at that time. It was intended by the designers to be developmentally appropriate and play-based with the primary goal of preventing the experience of persistent early failure in children. The EC was not intended to be a literacy and numeracy intervention, yet it did considerably alter pedagogy in these domains, particularly the age at which formal reading and mathematics instruction began. As part of a multi-method evaluation running from 2000–2008, the research team followed the primary school careers of the first two successive cohorts of EC children, comparing them with year-ahead controls attending the same 24 schools. Compared to the year-ahead control group, the findings show that the EC children’s reading and mathematics scores fell behind in the first two years but the majority of EC children caught up by the end of their fourth year. Thereafter, the performance of the first EC cohort fell away slightly, while that of the second continued to match that of controls. Overall, the play-based curriculum had no statistically significant positive effects on reading and mathematics in the medium term. At best, the EC children’s scores matched those of controls.