Sea sailing recommendations

My 17 year old son is a keen dinghy sailor.  He's actually just qualified as an RYA dinghy instructor.  But all his sailing has been inland and he has hardly done any at sea.  I want to send him to the seaside for a week or weekend at least to get some dinghy sailing in, this summer, just for fun so he can enjoy it instead of instructing, but I don't know where to begin.  I see there are advanced RYA courses in seamanship or racing.  Is that a good idea?  Or better to just let him hire a dinghy?   Are There residential centres he could go to on his own or should we take the family camping by the coast somewhere?  Is one bit of sea the same as another or are there better and worse places  within a few hours of London?  Are there any locations or sailing schools to recommend?  Sorry for so many questions, I'd just appreciate some ideas to start....

 

Nonsailor, you didn't say where you live, BUT at 17 your son would be welcome at any Kent schools event, don't be fooled by the Kent bit or the schools bit that's just historical. KSSA provide training & racing days/weekends around Kent for any U19 that can sail and has a boat, many are coastal and there is a great weekend camp at Sandwich bay on 11th & 12th July. You would however need to find/borrow him a boat.