The better question is where is the supreme court? While they have ruled that schoolrooms can be used for religious purposes, including prayer, after and before school as long as all student groups have this privilege extended to them, they haven't ruled on use of the room during school hours. They might well frown on it, but then again they may make an exception to accomadate them since the religion mandates that it's adherents pray at set times of the day.
My first thought is why not let them go outside to do it?
Another thought is to have the Muslim kids live on Middle Eastern prayer schedules. NOON in Mecca would be what time here?