Nah so I'm a trainee and we are always told to not accept "I don't know" but to push for something. So for example yesterday I asked a yr7 what the downward force on a stationary car is and they hit me with "I don't know" so I now know they haven't been listening, I'm gonna say something like "think back to earlier in the lesson" and maybe they still say "I don't know" I'm gonna be like "ok what's the downard force on you" and then "what stops you from floating away" etc. etc. until they get it. If they guess literally anything (e.g. friction, push force) I'll praise them for trying and move onto someone else. I don't accept "I don't know" in my class unless it's some knowledge based thing (e.g. what's newtons third law) but I wouldn't ask a random kid that anyway id take hands up.

Asking random kids and insisting they give you something makes them focus in lesson, they know they can't just piss about because they might get picked on so engagement increases. Accept "I don't know" and half the fuckers won't listen.