Try to use positive strategies rather than negative ones. The negative ones can backfire, causing kids to hate their schoolwork even more than they already do. Incentives (get that A+ and you get that bike!) are sometimes useful, but don't make the goal higher than is easily attainable by the youngster - you want a small stretch, but nothing that will end up demoralizing the child altogether. When you see the kids studying, make positive remarks and/or use the CLeaR Method of powerful positive reinforcement (see Raise Your Kids without Raising Your Voice). Don't discipline for marks; rather, if you decide to use discipline at all, use if for failing to study. For instance, if the child hasn't done a certain amount of homework/study that evening, then computer time can be suspended (and so forth). Help the child structure himself to succeed. Keep in mind, however, that when punishment is frequent, it becomes meaningless. Therefore try to avoid using negative consequences and instead, focus on the good feeling interventions first.  Sarah Chana

I never punish a bad grade. I encourage my children to do their best and make the whole school thing as positive as possible. I find that this works great.

If your child has bad grades, I would simply not give extra privileges. Like, if he wants a new cell phone or something but you see that he got a very low average grade, you can say, "I don't think you deserve a phone this term. Maybe next term, if I see those marks improve."

You need to set rules like in bed by a proper time, no parties or outings on school nights and all that kind of stuff so your kid can do his best in school. I wouldn't just let them do whatever they want and then hand out a punishment for getting poor grades. Kids need their parents to put their foot down. If anything, I'd give rewards for good grades as a form of encouragement.

beat their ass and tell them their lucky to be alive