School Issued iPads with Teacher Apple ID's that we want to reuse for staff and students

You need to obtain proof that the school owns the iPads - an invoice or purchase order with the serial numbers. From there, you can contact Apple for assistance. You will also need proof you are employed by the school, such as a pay stub.

~Lyssa

If the Apple ID is managed Apple ID (Enroll in Apple School Manager) I think that can be erase. If it is personal Apple ID. There are no way to bypass that because if you erase it, it will need to enter Apple ID and password. I recommand using MDM. I have tried different Free MDM. The best one is Mosyle (If there are budget limit).

If the iPad is set up using a school Apple ID: 

If your school has been managing the other ipads with an Apple School Manager or an MDM and these devices are enrolled into them, you can potentially wipe-off/ factory-reset the device and set up the device again using Apple School Manager. It is as simple as that.

If your iPads were set up using a personal ID, which you obviously have no hold of now,  you can try the following: 

Factory reset your iPads by connecting it with a lightning cable to a computer with iTunes app. In the iTunes app, you can choose to reset the device without backup. This will wipe the iPhone clean, erase all data using recovery mode. You can set it up again with a new Apple ID, this time preferably a school id. 

Next, add it to Apple School Manager (it’s a free offering by Apple) to secure these iPads and avoid such scenarios in the future. You have to contact Apple/reseller through which you had purchased these devices. They can authorize your ownership on the device. Once that’s done, you can add them to the Apple School Manager, where all the devices are set up using one single Apple ID, the school’s Apple ID. 

For managing the devices more effectively, applying policies against security and misuse you can manage them with an MDM solution. Choose an Apple MDM solution and add it to the Apple School Manager.