You smoke weed so that when It goes in to your lungs and gets processed it ends up in your bloodstream and travels to your brain and dopamine and shit just google it.
Basically breathing it is like smoking it.
Well, they might have brought about 5+ lbs of weed and lit it on fire in the ventilation system, so everyone inhaled the smoke. Although the smoke detectors would (should) have gone off, so the school would have been evacuated. Unless they prepared for that as well.
Basically breathing it is like smoking it.