The GATE program in PAUSD was cancelled a long time ago because of lawsuit. GATE only exists in paper so-call “differentiation education" within classroom, all differentiation takes place within the context of standards-based instruction in the regular classroom. Teachers enrich and extend the core curriculum for gifted students by differentiating instruction, content, and process. However, a lot of teachers don't have that because of increasing class size in recent years, unless they have classroom volunteer for helping. I heard Nixon school and Escondido offer differentiation at classes by volunteering faculties from Stanford.
PAUSD participants EPGY which opens to any students. You can register yourself online.