Tufty will always show off his venting ability once you get the first incorrect question. After this, he will only vent once you either counter him (like Marzia and Viktor) or the bell rings (doesn’t matter if it’s for break or lesson). The more notebooks collected makes the time he spends in the vents shorter.
Once he enters a vent, he chooses the vent closest to the player and eventually descends from that vent.
You can prevent him from using a vent (either entering into it or descending from it) by using a ventilation duct heater (works like the neodymium magnet). Be wary that it does fall off on its own after some time (within 1 to 2 minutes).
I won’t spoil the other mechanic he has or the items you can use on him.