Q: Activate ipad?

My kid has an ipad mini issued by school. He's had it for three years, no problems, no change of apple ID or password, etc. (with iOs 9.3.2, we think). Now, suddenly, after he slides to unlock and enters his passcode for the device, a screen headline pops up saying "Activate ipad" (which he has never had to do before); when he enters his apple id and apple id password to activate, he gets the message "incorrect apple id and [his specific email address] cannot be used to unlock this ipad". Apple tech. support (by phone) is stumped and directs him back to the tech. dept. at school; the tech. dept at school directs us back to Apple. So, as school is about to start again, he has an ipad that is useless. Can anybody help?