The most common use for high school codes is for standardized testing purposes. For a standardized test, such as the ACT and SAT, high school codes help to identify the secondary institution a student is attending or has attended.
Aside from being used for testing, high school codes are placed on students transcripts for secondary education transfers and higher education. The high school code is a way to catalogue and organize the various high schools throughout the country. As different high schools offer different course options, the high school code is helpful in cataloging various schools. The high school code also informs where standardized tests are coming from, and where test results should be sent.