You base that statement on school districts where? It looks like the Anaheim school districts which are closest to
Disneyland have either the week of March 23 or March 30 (the week before Easter) off. I believe someone already mentioned LA Unified is off the week before Easter. Some of the major school districts serving the San Diego area have the week before Easter off. Several northern California school districts have the week before Easter off. The school district in the town that I live in is taking the week of March 23. All but one of the California state colleges gives their spring break in March, many of them choosing that week before Easter. Most of the University of California college campuses will be taking the week of March 23 as spring break. So as far as local California based schools, I'm not really seeing any that are taking the week off after Easter. While people travel to Disneyland from all over, the bulk of visitors are from California. Furthermore, the rumored agreements that Disney has with the city of Anaheim suggest that they are to minimize their use of fireworks on weeknights during the school year so since the closest local schools that I could find are having spring break either of those last two weeks of March, that would make sense for Disney to choose to run fireworks then.