E-Readers within a School Environment

We recently purchased 6 Kindle Touch e-reader devices and then quickly returned them once we realized that they had no parental controls on the store or web browsing.  As a K-12 school, we all know the importance of monitoring the web and even book selections.

We are now in the process of looking into the Nook Color - again, parental controls are limited, they do have the ability to shut off web browsing, but the store is wide open (with a school credit card for purchasing) and students can still browse through the wide variety of book titles.

Has any other school faced these parental control issues?  Thanks in advanced for any contribution.