I know it sounds crazy, but toddler pool helped my son. When he was about 4 and refused to do anything with pool, we suggested him to go in the toddler pool, or warm pool on lap. We also spend lot of time just walking around the pool. After few days, he asked if he can go in the BIG pool. We also took him to pool with his friends. In the beginning he just sat on the step and watched them. I would second the private lesson; try to find someone your son will feel comfortable with. There are many books for kids which talk about water fear, which might help too.
From my personal experience I would suggest not pushing him to go in until he is ready. My son is now 6 and it is hard to get him out from the pool.
Good Luck!!
