Early years education has received considerable attention in recent years, particularly as a result of longitudinal studies that demonstrate the importance of the first few years in a child's development and educational experience. In 2004, a new approach to early years education, the Foundation Phase, was introduced in Wales. This is a major flagship policy of the recently devolved Welsh Government, and marks a radical departure from the more assessment-driven competency-based approaches to early childhood education that existed prior to the Foundation Phase. Studying approximately 2000 children in Wales who are part of the UK Millennium Cohort Study (MCS), all born in 2000-2001 we investigate the potential impact of the Foundation Phase pilot on a range of key academic and well-being outcome measures. Compared with other children, those attending a Foundation Phase pilot school tended to have lower scores in a number of academic assessments at age seven and lower subjective well-being, in terms of their attitudes to learning and well-being at school. We consider these surprising, yet concerning, results in the context of the methodological limitations to this analysis and propose how the MCS can be further used to substantiate these findings.