Read here a the recently published report by Dr Marlynne Grant:
Longitudinal Study from Reception to Year 2 (2010-2013) and
Summary of an earlier Longitudinal Study from Reception to Year 6 (1997-2004)
The Effects of a Systematic Synthetic Phonics Programme on Reading, Writing and Spelling –
with whole classes of children who started with the programme for first-time teaching in Reception (aged four to five years) and received small group teaching with the same programme for catch-up as required
http://www.rrf.org.uk/pdf/Grant%20Follow-Up%20Studies%20-%20May%202014.pdf