I taught him how to swim by holding his head under water as he struggled
I hope you are joking about this. Do you think that was the right way to teach him how to swim?
Well, he didn't drown so yeah, I guess
Holding your kid's head under doesn't teach your kid to swim. It teaches them pain and it's the wrong way to train him to handle the water. Show your child how to swim by protecting them.
School teaches the child how to be a zombie by spoon feeding. I want my child to be more self sufficient.
I think you were a bit too harsh when teaching this skill. You don't have to put a child in harm's way for them to learn things.