Running four mixed-age Montessori classrooms since 1975 under certified lead teachers, Montessori School of San Diego enrolls approximately eighty children ages three through nine on Spruce Street in Mission Hills. The primary program covers practical life, sensorial materials, language, math, botany, zoology, geography, and music, supplemented by piano enrichment through partners such as Dr. Kim Piano Academy. Elementary students ages six through nine add Spanish language, computer instruction, and research-driven projects that match the reasoning and abstraction stage of the second plane of development. Graduates completing the 6-to-9 classroom commonly transition into middle-grade programs across San Diego including Grant TK-8 School for fourth grade and beyond. The most advanced work happens in the elementary room, where multi-year self-directed research cycles build on the traditional Montessori albums under guidance from diploma-holding lead teachers.