How do you expect anyone to take what you just wrote seriously when there's such a blatantly obvious difference in the detectability of the use of these two different products?
up to a point the teacher's job is to notice these, and motivate the student to pay attention (report cards, detention, extra homework), or ask for them to be removed from class if they are disruptive, if necessary permanently.
The solutions are simple and effectively free. That's not the issue. The issue is nobody wants to do the solutions. Schools don't, parents don't, kids don't. Everyone is just lying to themselves.
You can't on one hand claim to care about kids and then on the other dismiss obvious tactics like banning cell phones.