the network for radical unschooling families
Deborah, if you're looking for information on local laws and proceedures, a local group will serve you better. There's a California Unschoolers group here in the Groups section. And assorted groups in CA listed here.
Generally, by the time a kid is 16 or older, you're running out of time for "unschooling" in the full fledged sense, because it takes a year or two for older kids to get school out of their systems (this is true of graduates as well - employers regularly report that it takes a year or two for graduates of high school or college to stop acting/thinking like students). So what you're looking for are ways for your son to opt out of school for the remainder of the compulsory attendence period. That might be online, charter schools, some kind of home-ed, or pure deschooling (which could include anything from working at a job to playing video games and sleeping a lot) the biggest issues are dealing with legal requirements on the one hand and supporting your kid so he doesn't feel like a failure ("drop out") on the other.