Many teens come to class trashed after late night partying and sleep in class, those not asleep are texting/playing games on their cell phones. My HS teacher wife fought these battles on a daily basis. Some teens lack motivation to learn therefor due to social promotion graduate HS functionally illiterate. I witnessed the result of this when I returned to college in the mid 70's, I was amazed at how dumbed down the classes had become. Just a moderate effort and you were able to easily ace most courses, far different from when I was in college in the mid 60's.
