I am not aware of any CA districts that offer summer school for anything other than remediation anymore. There may be some, but I don't know of any that do what my high school did, which was to allow students to get ahead by taking summer school courses. It's really a shame. I was able to clear out time in my schedule for more music and foreign language classes by taking history in the summer. I also was able to get back on track in math (didn't take algebra in 8th) by taking geometry as a summer course.
My children won't have the opportunity to do that. I assume it's because of budget cuts. CA schools are in bad shape.
DS '04 "Boogaboo"
DD '08 "Lilybear"