I was never grounded for it but my teachers did eventually get the message through my thick skull that I really couldn't miss homework assignments.
Now, in high-school, I am prepared for the work-load and get all of it done almost all of the time once I'm used to the routine again. You really should do it and never procrastinate unless you know exactly how much time you have and exactly how much time it will take.
Also I disapprove of still having the DSi, that's like taking the punch out of it.