Our son had a similar start to school, though not as extreme. You need to consider the teachers that your son would have and whether they can differentiate appropriately, otherwise the school experience is not going to be a positive one. You also need to make contact with whoever takes the classes when the regular teacher is on release time.
Also consider the timing of his move. It would be frustrating to move from the Year 2 to 3 if he had just made friends. From experience, the 'sorting out how things work' takes no time at all. The social takes longer.
You also have to accept that he is going to be bored at times and that primary schools here do vast amounts of busy work that he would be expected to put up with.
