Looks like its a standard apple MDM solution to me. I use a competitor called JAMF withing my job role for exactly the same kind of setup on school iPads.
I imagine what they will be doing is wiping, then enrolling, the iPad into this MDM, this will give them essentailly compelte control of the device being able to do restrictions, app install controls, and essentially control everything at device level with no way of overriding. In regards to signing in with a personal account, I have this completely blocked on most school iPads we provide. There's simply no need for a student to be signed into anything iCloud when we are pushing all the apps they require via that MDM. I'd wager they will do something the same.
The only difference should be the way it behaves when wiped. They will likely block the ability to use the "erase all content and settings" feature simply to stop students eaisly getting control of the device, but its how the devices behave when wiped that vary. All the devices we buy within our school are linked to "apple school manager". This is done by our resellers for us at the point of purchase. We provide them our school manager code, and they tie the serial numbers to our school manager at point of sale. We then use apple school manager to link them to jamf which does the actual controls. What this means is if someone were to steal one of our school iPads, plug it into a PC / MAc in recovery mode and wipe it (which can't be blocked no matter what). When it comes back to do the check with apple, it will still know it belongs to our school. No matter what you do it will check in with our MDM pull down all its settings and report its location agian. It uses the same technology as activation lock and theres simply no way around it.
We do have some odd old iPads reigstered that are not pre-loaded onto our school manager, and this is where things differ. You have to enroll those devices manually and how you do this has a couple of options. You can jsut do an on device enrollment. This is what I would hope your school would do really. The key difference with this is it can be wiped by the iPad user at any time simply by removing the management profile. You would loose all the managed apps / settings / wifi networks etc immediately, but ultimately you get control of the device back.
However, it's also possible to use a Mac app called apple configurator, to manually load a device into school manager. This then essentialyl acts as a proof of ownership of the device, and allows you to lock it down with activation lock in the same way. The only difference is you get a thirty day grace period where the profile can still be removed, and you can get ownership of it back. (see here
https://support.apple.com/en-gb/guide/apple-school-manager/axm200a54d59/web). If you dont remove the management profile within 30 days, the iPad then becomes tied to the instutitions school manager, and even wiping the device via recovery, or DFU mode, wouldn't realease it.
The school could very easily release it for you. There is literally a large "release device" button within school manager so it's as simple as searching for the serial number and clicking this, it literally takes seconds. However, even with me being the admin of all of this I describe, I wouldn't dream of having my childs personal device enrolled in any of this.
At the minimum I'd be asking the school to provide exact specificaitons of the settings they are going to be applying. I'd want the full policies and list of restrictions they intend to apply to the iPad in detail. Down to every setting (will the camera be on / off, will the app store be available, cna I still change notificaiton settings etc) as apple MDM solutions allow you to configure pretty much everything about the iPad. Even home screen layout can be locked down. I'd also want clarity on if they are doing a device enrollment, or adding the device to school manager. Then I'd probably ask them for their full GDPR data protection impact assessment on what information they are storing / gathering on the personal iPads.
At this age though I just wouldn't want to mix a personal use iPad with a shool use iPad in this manner. I think we all know kids push the limit of what they should be doing on everything they have, and having a personal device, subject to this kind of school control, is a recepie for disaster. I'd go as far as saying if the school expect to be able to control the devices to this extent, they shoudl be paying for them. My schools certaily do....... We'd never dream of making a student pay for their own then try and take control of it. This is what BYOD wifi networks etc are for. You lock down what the device can access in other ways, not by actually extending the controls to peopels personal devices.
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