Preventing changes to settings on iPad

Any specific ones you're looking for? You can set many restrictions in iOS through MDM and make the profile non-removable so they're stuck. This should do the trick for all the things Apple lets us manage.

Of course your students could always remove the MDM profile thus removing all of the profiles you've assigned to the device. To reduce the chance of that happening I would give the students strong incentives to keep the MDM profile on the device by rolling out something like WIFI settings via a profile.

There are also settings that MDM can't push that you need to set locally on each device, like blocking deletion of apps. You can set a restriction password to lock down certain settings.

The fact that apple hasn't updated the IPCU (and thus what MDM can manage) since iOS4 back in October, is a crime to the enterprise/educational market that has to manage these things.