If the issue is related to Safari/Clever clear History and Website Data:
Check another iPad to see if it’s working (it may be the site/clever you can always check Clever status at https://status.clever.com/. This is a great first step to see if this is a problem with the app or the iPad itself.
It's important to make sure that the iPad has a network connection.
You can try deleting and re-installing the app. Remember: you need to add the student's name back into the Settings, General, About, Name. First name, space, capital letter, of students last name, and a period. Sometimes if that is not done the apps will not download properly.
Rosetta Stone English is a large app (2 GBs). Some students' iPads may not have enough storage capacity to start/finish the download.
If these steps do not work, a factory reset through iTunes can work, but it is easier to just switch out the iPad..