LADUE, Mo. — A prestigious Missouri college preparatory school says it will discipline a group of students who exchanged a private series of racist, profane and sexual Snapchat messages that were leaked online to a wider audience.

The St. Louis Post-Dispatch reports that the Mary Institute and St. Louis Country Day School in Ladue began investigating after a student posted screenshots of the messages on Twitter on Sunday. The private school includes students in pre-kindergarten through high school.

In the messages, at least three different people used an offensive racial slur against African-Americans. Another user asked if anyone knew how to submit an application to the Ku Klux Klan.

The head of the school, Lisa Lyle, wrote in a letter Monday that she was “heart-broken” and “deeply offended” by the messages.