提上来说，Last time I checked, Ryan's statement was protected by the

especially if this is a public school.

He didn't tell others not to believe in Santa. He simply stated his own beliefs.

Of course it's up to the parents whether to continue this fight. I personally wouldn't. It's too complex for the child and it's counter productive. But if I did, I'd ask the teacher to show the guidelines, which are potentially unconstitutional.