Since 1899 a Seventh-day Adventist school has been available in the Pomona Valley/Inland Empire to those who want to give their children a Christian education. Pomona Adventist Junior Academy was opened in 1899 and Ontario Seventh-day Adventist Elementary School started 19 years later, in 1918.
Pomona Adventist Junior Academy began as a small church school with one teacher, Robert Sanders. In 1901 a new school was built at 7th and Cassell Streets in Pomona. The membership of the church grew and made it necessary to add classrooms. A new school building was built in 1921 at East 6th and Linden and operated at this location for 17 years. In 1939, the school moved to a new location where a new building was constructed on a large plot of land at 850 East Grand Avenue, and eventually a Junior Academy was added. It continued to operate at this location until 1990.
It was in September of 1918, that the Ontario Seventh-day Adventist Elementary School opened its doors for the first time. Class was held in a small room at the rear of the original church on Vine Avenue, which the congregation had added on. By 1923, an overcrowded classroom and fire brought about the need for a new school. A lot on Monterey Street was donated, and work began immediately on a new building, which was ready by September. The new school operated as a two-classroom, ten-grade institution with domestic science and woodworking rooms. During the summer of 1962, a new school plant consisting on a nine and one-half acre site located in the northeastern part of Ontario at 1722 East Eighth Street. The school has operated at this location since that time.
On May 20, 1990, a joint constituency meeting of the two schools voted to approve creating a new joint school in the Pomona Valley/Inland Empire. The two schools, Pomona Adventist Junior Academy and Ontario Seventh-day Adventist Elementary School, merged on the Ontario school campus. The new school started operations in September 1990 as San Antonio Junior Academy.
In the 2005-2006 school year, SAJA became SACS, San Antonio Christian School, upon joining the Southeastern California Conference of Seventh-day Adventists. SACS is still going strong today and Starting the 2016-2017 School year.