Bay Area school districts in San Mateo, San José and Marin have tightened cellphone restrictions in recent years. Bay Area school districts in San Mateo, San José and Marin have tightened cellphone restrictions in recent years. (Laure Andrillon for CalMatters)A new California law means school districts must develop new policies prohibiting phone use during school days. The Oakland Unified School District in June approved a cellphone ban on its 80 campuses, in line with a state mandate that took effect over the summer. Bay Area school districts in San Mateo, San José and Marin have tightened cellphone restrictions in recent years, and in 2024, Gov.