My dd is in Montessori upper(age 9-12) grade 4-6. .She says some of the kids *might* still believe,but it has not been an issue like it was for my ds in his lower class(age 6-9) grade 1-3 which had some serious pro-santa kids. I am glad my ds will be in upper next year where kids control their emotions a bit better about beliefs.
I'm all curious to see how this goes. He'll be in the older class post-holidays, right?
I do think you need to have it out with the principal and your ds's former teachers though. What did they do when the other kids were telling your ds he was "killing Santa" because he didn't believe? And what on EARTH was the principal thinking to call you up to pass on the other parents' complaints rather than telling the parents to teach their own kids tolerance?
I'm glad your ds will be out of it, but I doubt he's been the first to be bullied by the Santa-cult.