In 1913, the San Juan Union High School District was organized.

Dorothy Gertrude Jerauld, the first student to complete studies at the Grammar School, graduated in June 1914.

After Citrus Heights' founder Walter Trainor donated land, construction began on a new school at the current location off of Greenback Lane in 1915.

The original building was expanded in 1938, when work was completed on the "A" and "B" wings of San Juan High School, and two years later, enrollment had increased to 400 students.

[3] The San Juan Alumni Association was formed in 1980 and had 1,100 dues paying members as of 2011.