Hi PI-Support,
I work for a school district too, and asked my Apple SE about what to do when we get iPads back that are locked. He told me about a new process to make this easier:
Streamlined email process for removing activation lock
AppleCare has announced a new process to assist institutions with returned devices which may be activated locked. For customers who experience this for the first time please call AppleCare at 800-800-2775 so that the process and needed documentation can be explained. After the initial call customers can email with the required documentation for all Activation Lock Removal requests.
Other options include tracking down the person who previously used this iPad and have them follow one of the resolutions on this page: http://support.apple.com/kb/ts4515
Hope this helps and answers your question!
~Joe