As long as your athlete has not started regular season practices with his/her respective high school/middle school team, he/she is allowed to compete wherever/whenever he/she would like. Once an athlete begins regular season practices with his/her school, he/she is not allowed to participate in any events (tournaments/camps/practices) that are not associated with his/her respective high school/middle school program.
In other words, athlete is free to do as he/she wants until regular season practices begin and he/she steps foot in the room. Some athletes actually wait a week to begin school practices for this very reason.