The Missing flag is good, but if a student doesn't look at their grade report, they don't see it. Things that are Missing should go into the Overdue section of the course feed on the right hand side so that kids know they are Missing. Also, when kids turn in something that was Missing, it does not send notification to the teacher to grade it. Perhaps there could be some settings around the Missing flag that teachers could set to their preference, as some teachers may not issue the Missing flag unless students cannot submit the work late, while others may want to use the Missing flag as a notice to students that they should turn things in late.
Missing notification to students