On the other hand, maybe we do know - which is why many school districts are banning their use outright without leaving enough wiggle room for teachers to learn and teach how to use them wisely for educational purposes. Knowing that one half of local searches are performed on mobile phones must mean something about their value to the educational process.
Yet, the School District of Philadelphia has an official policy (adopted a number of years ago) of restricting everything related to electronic devices. School webpages reflect this policy across the spectrum: in elementary, middle, and high schools alike.
Here is the official policy excerpted from the 2011-2012 Code of Student Conduct.
That being said, denying students the use of a device that could be a powerful educational tool (in many respects) seems unnecessary and contrary to our mission as teachers. Instead of banning and restricting, we should educate and innovate. Just some possible uses I've read about are easy for students to comprehend:
1) Using calculator functions
2) Photographing important information (like homework assignments or finding geometric shapes in the building to analyze)
3) Using an App for an online management system like Schoology
Following the letter of the policy suggested would demand detentions or suspensions for almost every student across the District. Rather than relegate our children to a holding room, can't we support them in understanding proper use for these devices? In the long run it would probably create better karma when they are the ones running things.