My son didn't seem aware that he was hard to understand, it only really dawned on him when he started school, with the other kids saying 'what was that ' etc . he's very sociable and found it quite distressing at the time , fortunately he also has a thick skin.

I think that is possibly the biggest problem this causes.. frustration at not being understood. a lot of support was required at school for the first few years . getting in early is important, i must admit to being in denial about it.. the old 'he'll be right'' but it sounds like you are right on to it which can only improve things for him.