I dont know about the second part... but i'm sure glad I didn't jave illiterate trouble-causers in my class (as i did in elementary school (7-15yo)).

One such disrupter can take away easilly 10 minutes of a class hour, and 1/3 of the class not understanding basics, means the teacher has to try again and again to teach them the things they should already know, while the rest of tle class stagnates.