My son went to one of those chrombook-intensive public schools (though at least at the time they didn't start using them until 3rd grade; they start younger now).
Any time he had the chromebook out, he just played webgames. Not an exaggeration, he would go back on task when the teacher corrected then switch tabs the moment the teacher was not looking over his shoulder. I told the teacher to take the chromebook away if he did that and the teacher said "but then he can't do the assignment." The obvious reply was "he also can't do the assignment if he's playing games on the chromebook" but that somehow didn't compute.
We finally got him a plan under section 504 of the ADA that stated if he was off-task on the chromebook, then it must be removed. The teacher ignored this. We complained. The teacher still ignored it. We paid a lawyer to draft a scary sounding letter and the teacher finally complied. We sent his younger sibling to a private school.
I've heard parents say they "got a 504 and then had to pay a lawyer to enforce it" so many times. I just hate the idea of being forced into such an adversarial relationship with the school. In my life, any time we start talking about needing a 504 I think "we might as well just say screw it, because what good will come of this?" Like, in your story, I assume that while they complied, the way they interacted with your kid was tainted in some other from that point forward because your kid got them in trouble. Hopefully I'm wrong, but it's that kind of thing that I worry about for my own situation.
If it weren't so detrimental to his learning, we probably would have not pushed so hard. The good news is that it was his last year of primary school when this was a problem. The next year was junior high and he had 6 different teachers.
5 of these teachers had zero issues keeping him off of the device (now an iPad). The sixth was (from what we could tell) just not particularly gifted at classroom management in general. Anyway missing out on some unknown fraction of 1/6th of his education was much less of an issue than missing out on 90% of the classroom time (thankfully there were no chromebooks in PE or Music class yet; surely they'll find a way to do that too at some point).
Yup, that's the other factor; unless these computers are completely bolted down or tightly monitored at all times, kids will be doing other stuff. It's just too easy to alt-tab to something else.
And the worst part is that this isn't new. Back when I went to elementary school (early 90's) this already happened in the computer lab. A few years later my mom volunteered in the computer classes; one had internet, so naturally as soon as she turned her back there was a gaggle of kids around it to look at nudes.
But they haven't learned. And they got a bag of money post-covid to help kids catch up on missed classes, which they spent on computers and IT, and some opt-in external homework help.
Kids's attention spans (and their parents, for that matter) are all over the place, giving them any screen will just trigger their dopamine hit seeking automatisms.
I mean yes, everyone needs to learn how to use a computer - a lot of these kids didn't know what a file is - but make it focused, make it supervised, and lock these systems down.