Durham University academic Andrew Davis argues that it is harmful to make children who can already read when they start school learn phonics ("Imposing synthetic phonics is 'almost abuse', says academic", bit.lyPhonicsAbuse).
The problem with his findings is that, in my experience, these children tend to plateau out when their reading age reaches about 7. They do not have the necessary phonics skills to read more complex or unusual words, leaving them feeling frustrated as other children improve and move on. It would be interesting to know if their spelling was as advanced as their reading. My guess would be that it lags considerably behind; phonics skills are even more important for this.
Sara Wernham, Co-author of the Jolly Phonics books.