It IS legal.
Fundamentalists have been whining ever since 1962 that prayer was "taken out" of public schools. Nothing could be further from the truth.
Every September, hundreds of thousands of kids participate in See You At the Pole (SYATP), where they gather together and pray in a circle around the flagpole outside of the school.
There are numerous clubs and organizations that can be formed within a school. I went to a fairly small high school, but we had a Bible study club, Fellowship of Christian Athletes, and several other Christian organizations.
While in high school, I personally witnessed a person at school pray silently to himself every day in the cafeteria before he started eating. Nobody ever said a word to him.
Know your rights - schools are LEGALLY construed to allow students to form Christian Bible study groups and the like.
But SCHOOLWIDE school prayer - where prayer is proffered over the intercom - was rightfully struck down (was it in the '80s?). It's one thing to pray silently to yourself or in a group. But to assume, in our present time when our country is a cultural and religious melting-pot, that all the students are Christian, is wrong.
It is not the business of the school or the school board to continue where church let off the day before. Educating our children is the realm of the state, not religion, just as faith in God is the realm of the church, not state matters. That, ladies and gentlemen, is the separation of church and state.
But that doesn't mean that kids must leave their religion outside before they enter their school. As long as they are respectful of other people's belief (or non-belief) in God, there will be no problem.