We started Yasin at swim school at 6 months and he loves it - he's a total little water baby. We're giving it a break at the moment because the boiler where he was enrolled broke and it wasn't warm enough for our liking.
We've been to a couple of schools and they were all pretty much the same - small classes, half an hour lessons with singing and splashing. Alot of what they teach is also teaching the parents how to handle thier babies in the water so if your DH can go to a couple (maybe a weekend class) he might benefit from them too.