In California, children must be enrolled in school by the year in which they are 6 by Sept. 1st (so children with birthdays on Sept. 2nd would not have to enroll until the following year, when they are nearly 7). Kindergarten is not mandatory. Mandatory schooling ends on a child’s 18th birthday (whether or not they have graduated, though of course they can continue in school after that time) Students who have graduated high school may be done before the age of 18, as can students age 16 or older who have passed the CHSPE  . Public schools, including charter schools and ISPs, and tutored students are required to be in session a minimum of 175 days of the year, but there are no specific requirements for private homeschoolers to be in session a certain number of days or hours.
Legal options for homeschooling in California
- Charter Schools (local or online)
- Independent Study Program (ISP) or Home Study Program (HSP) through a public school
- Tutoring by a credentialed teacher (you or someone else)
- Private Satellite Programs (PSP): these are private schools
- Private school in your home
There are two non-profit, volunteer-run homeschool organizations serving all California homeschoolers.
- Homeschool Association of California (HSC) "serve[s] the homeschoolers of California in a wide variety of ways." For example, it provides legal, support, social, and informational services, including an annual convention and several camping trips. 
- California Homeschool Network (CHN) "monitors and responds to legislation which may pose a threat to homeschooling" and "inform[s] and empower[s] homeschooling families, educate[s] the public, and foster[s] community among home educators in the state of California." It also holds an annual convention.