It's a pretty dependable shtick. When addressing a group of students, I pause and reflect, then with great seriousness I tell them that I may have overestimated them. I might have expected that kind of behavior from a bunch of second graders, but third graders? Maybe my expectations were just too high. This tends to work well in most situations where you simply subtract a grade from your target audience, and then wait to see if they take the bait.
Which they invariably do. It usually starts with the most conscientious of the bunch: the ones who pretty much on task in the first place. Their friends fall in line pretty quickly after that, then the challenge is waiting to see if the wave of shame will catch up to the ones hanging from the light fixtures. Over the years, my willingness to wait out miscreants and their acts of elementary school defiance has increased exponentially. I have grown past the need to control every moment in my classroom. I recognize that by inviting these little agents of chaos into my room, I have come to understand, tacitly, that there may be a class period every so often that goes nothing like I planned and the fifty minutes I had so tightly planned and rehearsed may go out the window because there was a disagreement at lunch, or trouble at four square. These are the things over which I have no control. But it doesn't usually stop me from trying.
That is the reason for that management gambit. Since most of my young charges are in a great big hurry to show how grown up they are, the mere suggestion that they appear as anything less than their full grade potential is troubling for them. And, as I have said, it is amazing how well this tiny bit of manipulation works. Right up to fifth grade. Something about being at the top of the heap, looking down tends to warp the perspective a little. In my experience, your garden variety fifth grader is every bit as concerned with their social standing as the rest of the kids below them, but when you get them into a pack, the dynamic shifts. So impressed with their relative maturity, fifth graders don't seem to flinch as hard when called out for their relative immaturity. Instead, they seem to revel in it. Maybe it's as simple as having hung around long enough, they have reckoned that there are a certain number of things that grownups say just to get them to do things.
In which case, I may have underestimated them.
Always so much more to learn.