What are the California laws pertaining to people being on a school campus?

Read any and all trespassing laws. They generally do not differentiate between public and private property. Public property just means "owned by a government entity", not "I have a right to enter it".

I agree with Attorney Popovich. I write separately to make some additional suggestions. Review the school's safety plan and visitor's guidelines. Also look to see if the school has posted "no trespassing" signage with an eye towards its visibility.

To what end? What is the underlying issue? You will also want to check with County ordinances. Since schools are organized by county, most of the rules related to schools are found at the county level. Here are the general rules for public schools: If school is in session, you need a reason to be on campus (any part of the campus), a person who doesn't need to be there is, essentially, trespassing. Outside of school hours (or extended school breaks, e.g. winter break), a person can usually be on any publicly accessible area of campus (outside area) absent signs to the contrary or other measures to keep the people out (e.g. fences); but you can be asked (forced) to leave by security or the police (depends on county policy). For example, I am a runner. Occasionally, I want to get in a track workout. The only places with tracks are schools. Where I live, in Jefferson County, they allow the public to use the a school's outdoor facilities so long as school is not in session or there is some event, that is in the county code. However, in Denver county, they don't allow public access to the outdoor facilities (which sucks because Denver County schools have much nicer tracks, although the rule is not enforced routinely...but Denver does tend to have fences). I was recently in CA and I went to the local high school and had no issue running on the track (lots of "civilians" were there doing the same).