This isn't meant as a flame, but you are in for a very long road if you are already excusing their behavior when they are 6 and trying to pile the blame on others.
I agree with this. What surprises me most, though, is that the OP is a teacher.
Believe me, my DS (who never gets into trouble - well...at school) got in trouble a couple of weeks ago for being rowdy in the lunchroom -- as in "talking too loudly with his tablemates."

Even though I thought it was kind of silly (I mean, what kid doesn't like to laugh it up at lunch with his friends?), and his teacher and the principal both told me not to worry - that the teacher on duty gives detention for ANYTHING she can think of, I still respected the teacher's decision to punish my son.
I also thought the 2 days of having to eat lunch by himself was kind of excessive, but I never let my son hear what I thought. There are rules he has to follow (one of them being to keep his voice at a minimal tone in the cafeteria), and if he doesn't follow them, then he needs to suffer the consequences.
He needs to understand this, and I do too.
OP, as a teacher, wouldn't you rather deal with a student who has been taught (at home) to follow the rules and to respect authority? By making excuses - you are setting yourself up to become one of "those" moms and your boys becoming one of "those" kids. Surely, you don't want that?
I'm sure this was just a vent for you (and it's better that you vent here than at the school!), but I just think that you need to be careful with how much you defend your boys. I admit that I've used the expression "boys will be boys" - but that doesn't mean that I'm saying what they did wasn't wrong.
Good luck!