The Claretian Missionaries of the Immaculate Heart of Mary began serving at the Mission in 1908 and quickly made plans to open a parochial school to serve the predominantly Spanish and Mexican families of the parish. A two-story wood and plaster building was constructed and at the request of Father Michael Ornate, C.M.F., the Dominican Sisters of Mission San Jose agreed to staff the school. On September 8, 1912, four Dominican Sisters, with Sister Teresa Meyer as Principal, opened their doors of the two-room school to the community. The convent annals of that year recorded difficulties:
"One hundred thirty-five children, two teachers, no books, no blackboards, absolutely nothing. . . . . We have to make the best of it."
In addition, the convent rooms on the second floor of the new school house were not yet completed, and for the first month the Sisters had to commute by electric trolley from the convent at Sacred Heart parish in East Los Angeles. Eventually the Sisters managed to acquire blackboards and textbooks for the classrooms. In 1914, many of the children who attended the school were poor and hungry and as a result the Mission School provided free lunches, books, and tuition. In spite of these hardships, the academic and spiritual education of the children continued forward.
Over the next several years, San Gabriel Mission's enrollment grew so temporary bungalow facilities were added to accommodate the student body. In 1931, the oldest existing building, the Spanish-style arcade, was completed and dedicated. This added five classrooms, an auditorium, and cafeteria to the growing school. When San Gabriel Mission High School was completed in 1949, a new convent building was begun to house the additional teaching Sisters. Upon completion of the convent in 1952, the Sisters finally left the upstairs apartments of the original wood and adobe schoolhouse, although classes continued to be held in the downstairs rooms. In 1954, a third building was constructed and became the primary-grade wing of the school. Four years later in 1958, the original schoolhouse was torn down and replaced by the building that presently houses administrative offices, three classrooms, library, and computer lab. On September 8, 1982, a groundbreaking ceremony for a new Parish Community Center to replace the auditorium and cafeteria took place. The Parish Center is used daily by the school community for the hot lunch program.
Sister Sharon Dempsey, O.P. who previously taught in the Junior High for nine years, was appointed Principal in 2006-2007. As a Dominican Sister of Mission San Jose, Sister Sharon leads a lay faculty and staff of twenty members to continue to fulfill the dream of our founding Franciscan Padre Father Serra which was "to spread the Word of Christ in California."