The Foundation Phase (introduced in 2008) provides a developmentally appropriate experiential curriculum for children aged 3-7 in Wales. The Welsh Government commissioned independent evaluation (led by WISERD) aims to evaluate how well it is being implemented, what impact it has had, and ways in which it can be improved. The three-year evaluation utilises a range of mixed methods at a national and local scale. This is one of four papers focused on impact. It draws on 604 school and setting survey responses, 1,008 parent/carer survey responses, 37 Local Authority interviews, four non-maintained organisation interviews, and 357 practitioner interviews. (author abstract)