It seems to me that some of this issue and how to approach it really depends upon the specific child and his/her attitude toward authority.
Some kids are naturally resistant to authority. These are kids who might get in trouble somewhat regularly or are the "lawyers" who question every bit of every rule ever handed down to them looking for loopholes. When a teacher is wrong with this kid, it might be a good time for him learn some lessons about respecting authority and managing his tone to elicit good reactions from his audience.
But for other kids, those who start from a position of respect for authority and who pride themselves on following the rules, the experience of having a teacher who is wrong might be a good opportunity for them to learn to *challenge* authority. Blind obedience is, IMHO, just as bad for a kid as blind disobedience. I think our goal should be to try to get kids from both ends of the spectrum to the middle, where they understand appropriate times and methods for challenging authority.
This is such a great point! DD is a teacher pleaser(not completely sure where ds is going to fall--at present he's much more peer focused then teacher focused and rarely has anything good or bad to say about his teachers--however, I suspect he's going to lean more towards the argumentative side). It's been a slow process in helping DD see that it is ok to voice a disagreement. It doesn't help when (as with our avocado incident) the teacher fails to acknowledge the legitimacy of the view point, but weve seen her more and more willing to stick to her guns as she has matured. It will be interesting to see what middle school brings. I was a TOTAL teacher pleaser in elementary school and then had a teacher who so offended my sense of fairness in middle school that I lost all fear of challenging authority. In hindsight I don't regret challenging the teachers I challenged (the teachers I respected found me to be an active, respectful participant in class), but I probably could have let some things go that I didn't. Once a teacher lost my respect I looked for every loophole I could find--definitely more about my attitude towards the teacher than a reflection of my need for truth and accuracy

. Still, If I'm honest, I have to say that I vastly prefer my sassy middle/high school self to my sheep-like elementary self!
