If your update does not appear to start, restart your iPad. The installation should begin automatically within a few seconds. This issue can occur when you're using the App Store, Apple Configurator, or Mobile Device Management (MDM) to update.
If you can't update to Classroom 2.1 on an iPad with iOS 11
Learn what to do if your installation of Classroom 2.1 never starts, and the previous version remains on your iPad.