if the kid has no symptoms, and tests positive, it is a case to self isolate (the kid as well as the whole family) - so they don't transmit it to other kids and teachers who might be vulnerable. And in this case, it might very well be fatal to the teachers who are in close contact with the kid.

Why is this so hard to grasp? Being a disease carrier is a problem even if the kid doesn't show symptoms, especially it's been established that covid is transmissible with no symptoms.