Montclair High School is a high school in Montclair, California. It is one of the twelve schools of the Chaffey Joint Union High School District.HistoryMontclair High School is one of the oldest schools in the district. The school opened in September 1959 as one of the most modern schools in the area. The campus had two swimming pools and each classroom had air conditioning. Montclair High School's first class graduated in June of the following year in 1960.