Right now, it's not that easy to send a message to all users who have not completed an assignment. You can do this from the course participation report, but it would make more sense to do this from the Assignment module itself.
The assignment module has filters showing students. one of the filters is 'not submitted' and it brings up all the students that still have to submit an assignment.
Above the filter for submission, there's a dropdown menu that says 'with selected ....' and has a couple of options (download submissions, lock submissions, grant extension). What my teachers are missing is a simple 'send message' feature.
It makes much more sense to have it in this dropdown menu than to have it in the course participation menu (which doesn't work that well to send messages to users that haven't submitted an assignment anyways)
Would be nice to have this feature!