Today I covered 7th grade math (pre-algebra). The lesson plan instructed me to go over some problems about percents with them. No sweat.
Near the top of the period, a boy from another class came in. He was sent out of his class to complete an essay of some sort--probably a time out assignment. This didn't matter much to me. I gave him a spot in the back of the room and ignored him.
Then it was back to the class. And I had to figure out exactly how they were doing the percent problems. Sure, I could try to teach them to do the problems my way, but I'm only there for one day, and I'd rather not confuse them by teaching them a different method. By asking them the right questions, they gave me an idea of how they were doing the problems. It was a bit cumbersome, but I could deal.
The boy in the back of the room felt it was his duty to inform the class that there was an easier way of doing percents. Again, I ignored him.
We got through the six problems that we were supposed to. After we finished number six, one of the students stated that the answer I got was wrong. The boy had again commented, and the students sitting near him told me.
I asked what I had missed, and it turned out that the boy had missed one crucial thing--there was a decimal in the problem that he had not noticed. The class then came to my defense, berating the boy for questioning me.
These sorts of things don't bother me. I'd rather know if I made a mistake so I can correct it. But I think the boy thought he knew more math than me, and he was just looking for an excuse to correct me. Ah, such is the lot of the lowly sub.