Simon Gratz High School Mastery Charter, formerly Simon Gratz High School is a secondary school in Philadelphia. Its name honors Simon Gratz (1840-1925), a member of the Philadelphia Board of Education. Originally a public high school operated by the School District of Philadelphia, Gratz has been operated as a charter school by Mastery Schools since September 2011. Students from the previous public school's enrollment area are eligible to attend. It is the fifth Philadelphia high school operated by Mastery.

In 2012, the school was removed from the Persistently Dangerous Schools List while under the new management of Mastery. Part of the building is used for Mastery’s Prep Middle School (7-8th grade).