The flagship policy for teaching three to seven-year-old pupils in Wales has led to an improvement in standards of learning - but failed to make any impact on the link between poverty and underachievement, according to a major review.
Watch this report from our Education Reporter Tom Sheldrick:
The Foundation Phase, which focuses on pupils learning through play and experience, and spending more time outdoors, was rolled out to all Welsh primary schools in September 2011.
It is seen as one of the most successful reforms to the education system here since the Welsh Assembly gained responsibility.
Now, a report on the policy's implementation has found "overall improvements in children's educational achievement, wellbeing and involvement", and a link to improved attendance.
However, one of its key targets - tackling the relationship between deprivation and low attainment - has not been met.
Throughout school, pupils from poorer backgrounds perform significantly worse than their better-off classmates.
The evaluation of the Foundation Phase "found no evidence to suggest it has made any observable impact so far on reducing inequalities in attainment" at the end of primary school.
The report also said that a "substantial proportion" of teachers had initial reservations about the introduction of the policy, replacing Key Stage 1 for three to seven-year-olds, but the majority of school staff now believe it is having a positive impact.
Today's report is the final installment of a series, after evaluation of the Foundation Phase by researchers at Cardiff University and the Wales Institute of Social & Economic Research, Data & Methods (WISERD).
It has made 29 recommendations, including the need for improvements to teacher training.
The Welsh Government says it shows "the Foundation Phase really is delivering for our youngest learners."