Sixth graders may act dumb, but they’re vastly attuned to the stares and glares with which a teacher rules the class room. They can sense when they’ve got your attention, and when they’re slipping under the radar. When to pass notes, when to throw stuff at each other, and when to sit ram rod straight, faces like choir boys and girl scouts. Angelic coronas are swapped just as quickly for sulfurous fumes should you step out of the class room, or turn to scrutinize the board. 
So a teacher’s got to be sharp, leery, wary, on their toes. You’ve got to develop a sense for the currents and tensions that criss cross a classroom. Know who’s messing with whom, which direction the foul wind is blowing from the bully today, who’s liable to start clicking their pens, whispering and snorting should you let your attention slip.
Then whacka-crack! You turn and lash your glare across the room like a whip, lay it on to the offending punk. Like a laser beam of white hot lava power you transfix your victim, lay into them with a death glare, and pin them to the spot like a butterfly to their display case. Upon which you’re liable to receive a number of responses, depending on the wit and wherewithal of the offender.
The first reaction of a novice punk is to simply stare at you, frozen like a deer in the headlights. These kids are amateurs, not worth getting riled up by. They’ll stare right back, panicked, and then quickly look down, ashamed, abashed, without spine. They’re not worthy of further effort. A mere quick glance will subdue them.
A more experienced kid will immediately avert their gaze, and stare disinterestedly into the middle distance, suddenly pretending philosophical preoccupation with the intangible. If they don’t look at you, they reason, you can’t be staring death glares at them. The trick here is to stay locked on for three heart beats, enough that their disinterested gaze becomes strained, begins to crack. Then, just before they glance at you, you look away, having made your point.
Now, a sharp customer will start off with the philosophical middle distance, but not lock into it; rather, they’ll allow their gaze to wander slowly across the class and finally settle on their books, where they begin to read with earnest, sincere focus. Once they’re reading, they’re safe. Hard to beat this one: if you call them out, they’ll look up innocently, startled out of their reading. Accusations are met with wounded surprise. 
A level above that is the stone cold killer. You catch them vivisecting a pigeon on their desk, or thrashing and shrieking, and shoot them a warning glare? They’ll simply catch it and throw it right back. BAM! Suddenly you’re locked into a staring match with a pair of lifeless, souless eyes. A slight smile will curl their lips; they relish the confrontation. The class stills, grows hushed as the rest of the kids clue into the battle of wills. The attention serves only to strengthen the offender, not weaken them. For these students have no shame, have passed through the disciplinary system enough times to have no respect for it or for your authority as a teacher. What they want, what they enjoy, is breaking teachers like an experienced rodeo rider enjoys breaking broncos. You match their gazes at your peril, for each second you hold it serves only to affirm the stone cold kid’s importance at the detriment of your own. (How do you defeat this gaze? I find that pulling a Crazy Ivan is the best bet. Sure you break a few desks and scare the hell out of the innocent kid that gets pulled into it, but sometimes you’ve got to do what you’ve got to do.)
But the true professional, the real player, the student master, will elevate their resistance to an art form. They’ll notice your stare, startle, and then lean violently to one side as if avoiding a bullet. Immediately thereafter they’ll spin around and stare incredulously at the wall behind them, only to turn back to look at you, impressed by the imaginary hole your death gaze has blasted into the wall. Then they’ll wipe their brow of sweat, flash you a grin, and go right back to whatever it was they were doing, assured of success by your sudden inability to be mad. 
There’s this one kid has taken it a step beyond this. He’s learnt the ability to redirect my gaze onto other kids. It’s almost a Jedi thing. He’ll see me staring, and then, somehow, will turn and pretend to follow my gaze onto the closest kid. Whom he’ll then tap on the shoulder, point at their attention at me. I’ll of course be looking at them at this point, causing them to panic. He then backs out of it, shrugging apologetically with a shit eating grin, and goes about his way. 
And me? I of course give the innocent kid a detention. To do otherwise, following that performance? Hell. That’d bejust plain rude.