School codes for high schools can be found online using either the ACT or the SAT websites. Simply go to either site and click on the Registration tab. Once on the Registration tab, find and select the code or code search link.
For schools located in the United States, both the SAT and ACT websites require the state in which the high school is located as well as either the name of the city or the name of the high school. School codes are given to schools by the Educational Testing Service and are used primarily by college entrance exams.