While I have heard nothing but good things about BMW driving schools, I personally would have a very hard time swallowing the premium they charge. You could attend 3 two-day driving schools for the price of their 1-day M school. I am sure there are some reputable high performance driving schools in the San Francisco area.
I used The Drivers Edge. Based out of Texas and use three more popular tracks around here to hold their drivers schools. I would rate the experience as a 10 out of 10. Cost about $300 for a two day event, which is competitive. Instructor for the whole weekend, and classroom time. I plan to attend a few more along with other HPDEs.