When I was in school, all I wanted to do was read the Sitepoint forums and learn more about HTML / CSS / PHP.
I had one teacher that took me up on my offer to let me use the one class computer when my work was done and that's exactly what I did with it. Then other kids opted into my sweet deal and ended up ruining it by causing too much disturbance around it.
Back then, I always resented the fact that it was more acceptable for me to sleep during class than to read material on the computer. So I ended up sneaking on my home computer after my parents slept and getting 4 hours of sleep each night so that I would then sleep during school.
I would've KILLED to have a smartphone in my pocket.
Now, I'm not sure what the best policy is going to be, here. But I can certainly relate to the injustice of feeling punished for something that doesn't apply to me.
I can certainly understand that a smartphone in the hands of a student will only make distraction more likely. But to take it away completely seems to overestimate the value of being attentive 100% of the time in school.
For example, imagine if you can take out your smartphone when you're done with your work AND you are averaging above a 85% in the class. Maybe something like that would offer best of both worlds.