Over the past few weeks, many users have been reporting issues with the Google Classroom and Google Drive apps on iOS. Most of the issues had to do with access to files:
Today, 10/2/2015, Google released a brand new Google Classroom app and Google Drive app to address the issues so many were experiencing.
The recommendation is to delete both apps from your iOS device before installing the updated apps.
Updated Google Classroom App: https://itunes.apple.com/us/app/google-classroom/id924620788?mt=8
Updated Google Drive App: https://itunes.apple.com/us/app/google-drive-free-online-storage/id507874739?mt=8