Look over their homework and make sure they are doing it. Call the teacher to check on them. You might be pleasantly surprised. Do not bad-mouth the teacher in front of your child. Assume the teacher is correct.
Kids sometimes have another story.
Attend your child's recitals, games, programs. Go to parent-teacher conferences, no matter what. If you can't go, call the teacher. Set aside homework time each night. No TV until homework is done.