My son's teacher told him that if he didn't behave he wouldn't be allowed to stay in Pre-K. He told her that that was fine because there wasn't anything that she was teaching that he didn't know. We don't tolerate sassy remarks like that at home but that might give you an example of what his school has to deal with.
Was your son being sassy or was he being honest? Or both?
I teach my DSalmost5 to be mindful of his tone and his attitude. Like you, I am trying to raise a polite, respectful kid. There are times when my ds crosses the line into rudeness and I check him on that. There are other times when I can tell that in his mind, he is just stating the facts or giving his opinion.
Random example "I don't want to spend the day with X, I want to spend the day with Y". On the one hand, if X was in earshot that statement could hurt X's feelings. Depending on the tone and intent that could be a very hurtful statement. On the other hand, DS is being honest and clear about his preferences.
Not the best example, but hopefully you all see what I mean.
As parents, we teach them to monitor and adjust. For me, that doesn't change the validity of his orginal statement. He should be able to express his feelings about where he wants to go and who he wants to go with. I am the parent and I make the final decision, but I want my DS to feel comfortable in voicing his opinion (
and know how to do it respectfully).
I can't imagine being a 5 year-old and (in the average traditional classroom) have very little say in what I get to learn.