I keep coming back to what I wrote earlier about some adults (teachers included) having a certain smugness where this issue is concerned. They generally fall into one or more of three categories. (1) They either never believed in Santa or have chosen to not do so with their children and internally (at a minimum) roll their eyes at those of us who do. They truly believe they know better than us and you can pretty much see the condescension dripping from some posts.

(2) Those who believe Santa is a "lie"......to some extent, they seem to think him an evil, cruel lie perpetrated on innocent children and that Santa is bad, bad, bad. Or as bad as an unreal person can be.

They can be a little rabid. (3) Those who believe children who have reached age X are certainly old enough to know the "truth" about Santa and if they do not, then they should....for their own sake......be enlightened as to the truth. Ahhhhh.....The joy of being a do-gooder who crushes a child's happiness.
Smugness doesn't even do it justice. Often, there is an air of superiority to it. "They" know better than the children and certainly better than we pro-Santa deceptive parents. If we won't snap our kids out of childhood and into the real world of adulthood on their timetable, by God they will do it for us. And they will pat themselves on the back for their efforts.
Well, no thanks. You teach your kid your traditions and I'll teach mine. I won't shove Santa down your kids' throats and you keep your hands off our Santa, especially if you are a teacher who is teaching a subject that could easily be taught with ZERO mention of whether Santa is real or not. You can assume all you want regarding what percentage of children of what age still believe in Santa, but I promise you it varies from one place to another and your assumptions won't hold true across the board. As I said, in my town the vast majority of 4th graders are still firm believers. There is no freaking harm in that. Here, the elementary school goes until 6th grade and the kids tend to stay kids longer, if only in some ways. Santa is one of them.
As one poster said, Santa is a vital part of the Christmas tradition for many families and almost sacred. Unless a teacher is clueless, he should realize that is the case with MANY Americans and leave the subject alone unless there is an absolute need to address it in the curriculum. And in elementary school.......There isn't. You can say 10 miles away from the subject of "Santa: Myth or Man?" with ease. In simplest form....It is not the place of the teacher to ruin the holidays for so many families. And it wouldn't be appreciated. Some said their principal would be annoyed if a parent came to them with this issue. I beleive ours would be thinking of the teacher, "WTH were you thinking, telling the kids about Santa like that? Now I've got umpteen upset parents calling me, telling me that you've ruined their upcoming holidays and I have to deal with the fallout. Thanks for nothing." But then, she's a mother of young kids. Many of the other teachers are too. I doubt they'd be on his list of supporters either.
My question would be, is he just a clueless yapper or is he one of the smug sort who feels he is doing the kids a favor by enlightening them? Sometimes it's hard to tell. But we can see by the posts here that there are many "enlighteners" out there. Why let a little thing like upsetting children and ruining Christmas for them stand in the way when THE TRUTH and FACTS need to be beaten into them? It's because certain things aren't appropriate at certain ages be they fact or not. Certain issues are the domain of parents until a child reaches a certain age. Traditions are to be respected, not made light of. And above all, a teacher should possess a MINIMUM of sensitivity and think before they open their mouth regarding issues like this. That's just common sense. Discretion is a useful tool. Teaching is not merely about facts....You should know the kids and care about their feelings. If not, you're in the wrong profession.
Again....Would I go to the principal? Well, if he was truly sorry, realized he was messed up and promised to not do it again, maybe not. But after talking to the teacher, if I thought he was a smug enlightener, you bet I would. Enlightening works both ways.
If this thread has done nothing else, it should have taught us that this is a hot button issue and as such, needs to be left alone by teachers of elementary school children due to the potential for emotional harm. But only a person who can see beyond all-important "facts" and also respect emotions and traditions will be able to see that. I don't hold out much hope.

Enlighteners are on a mission, whether anyone wants their "help" or not.