Testing on the iPad?

I'm looking for tools that allow students to take tests on their iPad or iOS Safari friendly.  I would love something centrally managed that I could import all the users and was easy for teachers to add and manage tests and questions.

I've played with Google Drive and Quizstar, but I would like something more.

I can't find it and so I am hoping that one of you may have glimpsed this elusive product. 

Any suggestions?