Best method to backup iPad data.

Managed Apple IDs from Apple School Manager have 200GB of iCloud storage.

https://support.apple.com/en-us/HT205918

Here's what is backed up with iCloud Backup:

https://support.apple.com/en-us/HT207428

Essentially it's anything that is not already stored in iCloud.

The last school district I was in only allowed the G-Suite for backups after using iCloud for years. There were many problems with third party apps because they do not back up to Drive by default. Some have to be configured, some do not have external backups as an option because they rely on iCloud. Many students lost their Book Creator projects when we switched to Google only.
I know some of our neighboring schools had success using both iCloud and Google together. Dropbox can also be an option you can add into the mix.

@tomhastings , So G-Suite backups work well with iPad backups? That would save the work of creating managed Apple IDs since they already have G Suite accounts.

I'll have to look into this.

Thanks

If you're using Powerschool, SunGARD eSchoolPLUS, or Infinite Campus, making managed Apple IDs for students faculty and staff is automated:

https://support.apple.com/en-us/HT207409

If not, but you have the data somewhere, you can upload student, staff, instructor, class and location data from .csv files.

https://support.apple.com/en-us/HT207029

msnowdon, yes and no. The overall iPad backup (that is described here: https://support.apple.com/en-us/HT207428) can't be saved to Google Drive.
App data such as Notability need to have the backup configured in the app settings to point to Google Drive by the end user, it is not automatic so there is always the risk of data loss. I have had too many students lose work because they did no turn on the backup feature within an app.
I would explore the apps that your end users use the most to see if they allow external backup options. Our director banned all Apple apps except for iMovie. For students to backup iMovie projects they had to make sure they saved projects to the Photos app. Google Photos was then used to sync between Apple's Photos on the iPad and Drive.
I guess you need to see what is best for the end user. I pushed for the Google and iCloud backup because it taught the students to explore the options that were available and allowed more app variety. Creating the managed Apple IDs in bulk is not too difficult, using those accounts to backup to iCloud is something that I was not able to explore. Hopefully someone with experience can chime in on that topic.

As I said, the Managed Apple IDs for education include 200GB of iCloud storage. When combined with iCloud Backup for iOS, this creates the most seamless experience for the end user. Ideally, they sign into their Managed Apple ID when they are completing Setup Assistant on the device, in which case they are automatically signed into iCloud and backup is enabled (where the device backs up every 24hrs when connected to power and WiFi). If the device is lost, stolen or broken, the end user simply signs into the replacement device with their Managed Apple ID and are presented with the opportunity to restore from their most recent backup. Within a few minutes, they are back where they left off with the previous device.

As a side benefit, if your staff and/or instructors are 2:1 (a macOS and and iOS device), they can enable Desktop and Documents in iCloud Drive on macOS. With these two folders in iCloud, if the macOS device is replaced, they should get most of their important files back on the replacement device automatically. This can be a significant benefit for most users because, as we all know, most users will not back up their important files on their own. 200GB of iCloud is plenty of storage for most users (certainly if their device has limited internal storage (e.g. 128GB or 256GB SSD).

Desktop and Documents in iCloud:

https://support.apple.com/en-us/HT206985

We have been using iCloud backup with managed AppleIDs, however it does have a lot of limitations, many apps won't backup their data to iCloud and even some Apple apps (I've seen iMovie and iBooks) won't backup files above a certain size. For the case where a device is damage and needs to be replaced I think we will switch to iTunes/Finder backup. Obviously a cloud based solution is needed for routine backups of devices to protect against device loss or a failure that prevents the device from syncing to a computer, but nothing seems really adequate here. I don't understand why Apple doesn't allow full device backups to iCloud.

We can't encourage users to manage their own iTunes/Finder backups because the restore process doesn't work properly if you restore to the same device on DEP.