Having taught for 34 years in SFUSD, I NEVER heard this mentioned regarding the public schools "requiring" boys to swim nude. Pat C. is older than I, and he is offering what I had always heard: The Downtown YMCA had a "trunks optional" policy at their pool. This was not SFUSD facility. The pubic schools did have a policy that because San Francisco was surrounded on three sides by water, being able to swim was incorporated as a high school graduation requirement for boys and girls. But that is the only requirement I ever heard about. This topic seems like a strange mixture of a "graduation requirement" and a tradition in a private organization, the YMCA.