J.F.
Welcome to Lafayette! It's been quite awhile since my kids took swimming lessons but the ones that clicked for them were the ones at the Contra Costa Jewish Community Center in Walnut Creek. I've also heard people in my Gymboree classes talk about the Sherman Swim School. I think the Sleepy Hollow Swim and Tennis Club in Orinda also does classes for non-members.
People in my classes also talk about Oakwood but I don't know if you need a member to do the lessons there.
J. F.