MacOS – Shutdown prompt keeps popping up

Your issue is in Macbook's powering.

If you unplug the power adapter and then reinitiate connection to the monitor by either turning the monitor on/off or replugging the Display Port cable, you'll see signal restored.
After that you can plug the Macbook's power adapter back again and it won't turn black for hours or even days (unless you use cheap "Chinese" power adapter -- that can blackout every 30 minutes or so). The only issue remaining is that if you use custom calibrated color profile after such reconnection the color profile resets and you have to open Monitor settings and just open the Color tab to reapply settings -- you probably can make an Automator script for that routine and bind a keyboard shortcut.

I've noticed that monitor can go black when my fridge in the next room turns on, so it's definitely about power. Seems like Macbook passes some bad electricity signals from charger to the Display Port.

"source": my comment to this thread http://en.community.dell.com/support-forums/desktop/f/3515/p/19658656/20922700#20922700

To solve data corruption, have users log out. Also, empower users to know if their backups are current and make it their responsibility to self-service restore activities.

To minimize restart times, have users restart the macs and sleep them when the login screen arrives (assuming you don't have auto-log in enabled). This makes much more sense to me since new classes should have everything prepped and the last class should clean up their mess.

All your workarounds seem like IT taking the cleanup burden from the users and also shouldering the data protection lead. When IT is seen as a second fail safe to be relied upon when the routine maintenance and operating throw an exception, your life will be much better. In turn, the staff and student's lives will be much better since you can then support the real problems and not be self-selecting and volunteering for all the janitorial work.

Also, having reboots be a monthly task is working well in most environments I'm aware of. If your software selection and testing is yielding leaky and crash-tastic performance, documenting that would be an excellent investment in the future so that the curriculum reflects the costs of maintenance since you are well aware of how real they can be when you don't have stable OS that can wipe things clean once a user logs out.

When IT can be responsible for system stability and users responsible for user maintenance (log out and log in) and you can track reboots as a signal that users are not trained or that a quality defect has slipped past the testing group, life gets far more fun for IT.

Lastly, look at your MDM provider - with 150 macs under management, you'll reap significant benefits if you learn how to use that tool proactively. If you don't have one, start a bushel trial immediately and reach out to one or more vendors to learn how you can leverage tools to assist. Even if you end up rolling out scripts to tweak hooks, you'll want a solid framework for monitoring and change management rather than laying hands on every cart and interrupting staff constantly for inevitable changes and updates.