High Quality Content by WIKIPEDIA articles! Sage Hill School is a private independent co-educational college preparatory school for day students in grades 9-12. The school was founded in 1999, the first year it filed a Form 990 with the IRS. According to its 2000 Private School Affidavit filed with the state of California, it opened in September 2000 with 35 Sophomores and 115 Freshmen. Today the school has grown to over 450 students in grades 9-12. According to the 2006 Private School Affidavit, the Freshman class for the 2006-07 school year has 121 students, less than the 122 Freshmen in 2002 and less than the largest Freshman class of 126 in 2005.