Spinnaker might be great - I don't know them - but if you're in the market for sailing lessons in SF Bay I can highly, highly recommend Club Nautique out of Alameda[1].

The quality of instruction is very high, with a focus on safety and building a strong foundation of knowledge. Especially if you ever might want to charter in remote locations or sail across oceans, it's really an excellent foundation.

[1]https://www.clubnautique.net/school/introduction-to-sailing/