If you use any app on the iPad that has students log in through Google and notice that the list of google account logins is at the max thus preventing students from logging in (or you just want to remove students from previous years), here is a fix to remove the old accounts from the iPads:

PLEASE NOTE: The process is a little monotonous 😃. It may be helpful to walk students through the process and have them do it for you on the classroom iPads after they log in with their credentials! 

On each classroom iPad you want to remove previous accounts: 

1. open safari on the iPad and go to google.com
2. click the sign in button in the top-right corner and sign in with a google account
3. click icon in the top-right hand corner and sign out
4. click 'sign in' again
5. the ability to remove accounts is now available
6. unfortunately there isn't a way to remove accounts in bulk. You have to click "remove an account" before each time you click the "minus" sign to remove an account.