I used to teach swimming so I've not enrolled in a class however we swim at least every second day, DS adores it. We practise getting into the pool, back float, kicking, getting face wet, splashing, blowing bubbles but most of all it's just about having a good time and building his confidence in the water.
Re: swimming
what kinds of things do they do? we have had one class so far
We started at 6 months and she loves it!
ETA: We do back and belly floats, go after toys, practice moving her through the water and getting her ears wet.
This. We go twice a week, and have for about two months. DS LOVES it.