Swim lessons for teenager?

My son enjoys the water but never really learned how to swim properly and can not tread water, though I’ve tried to teach him myself. He needs to become a stronger swimmer before summer because of a surfing program he’ll be doing at his camp. My guess is that he needs a series of private lessons with an experienced, skilled, compassionate instructor this Spring. We are in Berkeley but are willing to take him elsewhere if need be. Any ideas would be much appreciated!