H.B.
I also second Aqua Kids! My DD took her first lessons last summer at 4yrs old and she was the only one who cried and didnt want to get in the water. It only lasted for one class then she was in there with all the others (she has always been sort of dramatic about new situations...getting better though). The swim instructors and staff are awesome and didn't pressure her.
If you do decide that a swim school isn't so bad, I would recommend enrolling your son in the two week swim camp if you can. It is 30min everyday for two weeks excluding Sat and Sun. This way he can get used to the water and routine easier.
Good luck!