See if the activation lock remove option is available in JSS for that device. Depends really on how long ago it was supervised, and what device. Otherwise call Apple Enterprise and they will work on getting it unlocked with you. They are much faster now.

Ignore.

The bypass code is available from the Management tab of the device record. This is available for supervised devices. If you have this, you can restore the iPad as qhel373 mentioned. When activation lock comes up, leave the apple ID blank and use the bypass code as the password.

If this doesn't work or the bypass code is unavailable, the only other option is calling Apple Enterprise (or Education). It's a pretty painless process if the devices are institutionally owned.

I've had to do what Lewandowski has mentioned a few times due to students who have left the school with their Apple ID still on their device. Calling up Apple and let them know the situation, they will ask you to verify a few things and thats that. Wipe the device again and you should be able to give it to another user then.