Page 499 of the admin guide suggests otherwise...
If you want to force an app on an iPad you have to assign it via managed distribution so that it shows up in the purchased section before you can have it silent install. Otherwise it will prompt or you will get an error.
We use both methods. We have a testing app all students have to have installed. I assigned if through managed distribution (some kids have auto install on and it installed automatically), then waited a day so it made its way to all Apple ID's, and then created an app assignment to push it to all students. The few that it auto installed on I got an error that the app is already installed. The ones it didn't the app installed without prompting. We also use self service for them to install other apps they need but are not required to have.
Our middle school students do not have the app store. So all apps are assigned via managed distribution and an app assignment is created to auto install the app. Works without a hitch as long as the apps show up in purchased. Usually I wait a day to make sure they all get the vpp assignment before pushing the app.
