The message said: "Sonali Rodrigues, Will you go to the prom with me? HMU -Tate." HMU means hit me up, or call me.
Rodrigues said yes. But Tate and his two friends have been given one-day in-house suspensions by the headmaster and barred from the prom.
Tate tells The Connecticut Post newspaper he was told posting the message constituted trespassing and posed a safety risk.
Headmaster Beth Smith hasn't returned a Tuesday call from The Associated Press seeking comment.