You present a very interesting venture, which theoretically solves a lot of the concerns expressed by teachers as they attempt to integrate technology into the classroom. The Sentinel app seems like a very useful tool, however it has some direct competition from Apple with the Release of iOS 9.3.1, which introduced Classroom (https://itunes.apple.com/ca/app/classroom/id1085319084?mt=8), an app designed for teachers to share and monitor student work on Apple devices.
I currently run a 1:1 iPad program and will be introducing Classroom in September. Where we have run into difficulty is in our senior level grades where we use a BYOD model for technology. It would be great if Sentinel could function across platforms and monitor different types of devices at once.
I like your idea and would be interested in learning more.