I subbed in a third grade class today. Over all, I'd say it was pretty average, except for the fact that these kids were really smart. I mean, it was shocking at first. They were also almost too well behaved. The students started and ran their "morning meeting" (a feature common to most lower elementary classrooms) without any input from me. All I had to say was, "alright, let's move over to the calandar," and the student of the day took over. The kids then proceeded to do things like give squared and cubed numbers (along with square roots) in order to find different "number sentences" for the number of the day (14).
Later, during language arts time, we had a review worksheet on comma rules. They had a better understanding of comma usuage than many adults that I know.
I feel that I should also add -- they thought it was hilarious that I didn't know how to do the "three box method" of subtraction.