This is just out of curiosity. Looking at children in reception, some learn to read really quickly and others after 2 terms are still struggling with the one letter sounds. I know that many countries start formal learning later. Is there any evidence (for reading English) that those children who will spend the next couple of years struggling would do better or worse if they started at 7?
Hopefully they learn something between 4 and 7. I've not seen a struggling group being taught, but I'd find it stressful learning something I found that hard and I wonder if the gain from starting early is worth that.
Also, is there some sort of 'readiness' that comes at different ages for different children, or would those not ready at 4 still not be ready at 7 without some sort of intervention?