We tried several different programs for our five year old with PDD-NOS.  We had the most luck with the City of Allen's swimming instruction program.   My son has completed two different sessions of swim lessons--both times in the group setting.  (We registered him for the 3-4 year old classes when he was five, since it was a better fit for him.)  The instructor placed him in a small group with three other kids--all typical.  The instructors are wonderful, and if you tell them about your son's issues in advance, they can probably pair him up with a good instructor.  I was told all of the instructors (mostly teenagers) have training in dealing with kiddos with special needs.

Also, the City of Allen offers private lessons, as well.  We didn't need to go that route with our son, but at least it was an option if he couldn't handle the group setting.

Hope that helps!

:) Heather