Since there's no statewide school calendar in CA it's tough to try and plan around school schedules. Besides, I think some neighboring states can affect crowds as much, if not more, than local districts.
When we lived in AZ and made
Disneyland trips during school holidays we always ran into people we knew, sometimes lots of them.
And I swear it seems Utah license plates can outnumber CA plates around DLR during their school breaks. OK, that might be an exaggeration, but there's a definite impact.
As someone else already suggested, if you're trying to gauge potential crowds I think it probably makes more sense to pay attention to when lower level APs are blocked than to school schedules.
Oh, and I know CUSD, SVUSD, IUSD, and TUSD (all So OC districts) started after Labor Day this year. I don't know what their schedules look like for next year, but most districts tend to stick to the same before or after Labor Day schedule from year to year.