I took a precalc class with my son last year to help him get through it... I see him checking his "texts" on his cell phone under his desk while the teacher is giving a presentation...
I tore into him after class on the way home telling him how disrespectful it is to the teacher, and how he should pay attention so he learns what he's teaching, and if I was the teacher and caught him doing that, I would not answer any questions from him telling him that he should have paid attention when I explained it the first time....
It lead to a big fight - but sometimes you have to be a parent before being their friend...
He knows to respect teachers - his grandmother is a retired college French teacher (type A personality to boot)... She would back me up 100%... He respects his grandmother and should give other teachers the same respect...