Remind them that learning isn't always fun. There are no shortcuts to excellence. Most kids' TV, movies and video games have programed them to expect everything to be whistles and bells, spoon-fed entertainment. Sometimes learning something new is a cinch, but usually it isn't. Assign regular household chores.
Chores teach kids to see jobs through to completion and to value their place in the family unit.
Remember whose homework it is. The responsibility rests with your child to bring it home, to do the work and to see that the work gets back to school. Don't undermine the teacher's discipline procedures. If your child doesn't complete her work, don't make excuses or write a note explaining why she deserves an extension. Maybe she'll have to miss recess or a field trip.