It's not straw man cause that's exactly what kids do, they are not stupid and let you see their 2nd device. every time you confiscated something highly sought after, they get smarter and better at hiding, finding excuses to get a peek at stuff they want. I don't know which era you come from but from my high school year/region you can get expelled possess indecent material(like playboy magazine) and people still manage to sneak in and hide at some secret spot. If you are in the "club" you get to know where to check it out. And people go "poop" for extended time back then. What? You gonna stop them to go pee or poop?
Even if you TSA setup the entire school, if the class is boring there will still be no engagement, now what? Gonna blame the student is just bad and drop them out?
The entire preface of no phone == no distraction is laughable. And yet what's your solution about stop bullying? Remember that's what trigger the whole discussion? I guess you don't care since it's less harm done.
Oh, yeah, almost forgot, the guy I mentioned above that find spots to hide magazine later graduated from top university in my home country and still kick ass in his domain leading about 50 people sized team. Who knew the quick thinking and strategic minded can be applied in real world, right?