Just a quick FYI
If you have Google Apps and are running iOS and your Google Classroom app is configured to Auto-Update, then you'll want to stop it. The latest update v2.2017.06206 throws an error on launch "You can't use Classroom with this account" and that the user "isn't a G Suite for Education account". This is an erroneous error - press Ok and then X out of the next screen to choose accounts, and the currently logged in account CAN work. The process repeats itself the next time you get into the app.
We have an escalated ticket with Google but create your own if you get bitten.