Motivation for good grades eventually comes from a desire to please the teacher and parents, be admired by peers, enjoyment in knowing things, ability to see studying as a pathway to a future career, knowledge that they need a 3-point grade average to get into college, and self-criticism when they fall short of their goals.

Some children get into bad habits with their homework because they become preoccupied with TV programs, video games, or nowadays, Instant Messenger. Some middle school children become sidetracked by their hormones or by sports. Other children who find schoolwork difficult would simply rather play. If parents help these children cut back other activities to reasonable amounts and count on the teacher to grade the child's efforts on schoolwork and homework, most of these children will improve. Limit TV until schoolwork improves. While you can't make your child study, you can increase the potential study time. Eliminate all TV, video game, and Instant Messenger time on school nights. Explain to your child that these privileges will be reinstated after the teacher report or test confirms that all homework was handed in and the overall quality of work (or grades) is improving. Explain that you are doing this to help them better structure their time. Remember that TVs should not be allowed in the child's bedroom under any circumstances; let them read a book or listen to music instead.

Consider adding incentives for improved schoolwork. Most children respond better to incentives than punishments. Ask your child what they think would help. Some good incentives are taking your child to a favorite restaurant, amusement park, video arcade, sports event, or the movies. Sometimes earning 'spending money' by working hard on studies will interest your child. The payments can be made weekly based on the tests and homework reports. A's, B's and C's can receive a different cash value. What your child buys with this money should be his business (for example, music and toys). Rewarding hard work is how the adult marketplace works.

Remove other privileges for fall off in schoolwork. You have already eliminated school night TV viewing because it obviously interferes with studying. If the school reports continue to be poor, you may need to eliminate all TV, video games, and Instant Messenger time. Other privileges that may need to be temporarily limited should be those that matter to your child (for example, telephone, bike, outside play, or visiting friends). If your teenager drives a car, this privilege may need to be curtailed until his grades are at least a 3-point (B) average. For youngsters who have fallen behind in their work, grounding (that is, no peer contact) for 1 to 2 weeks may be required until they catch up. Avoid severe punishment, however, because it will leave your youngster angry and resentful. Canceling something important (like membership in Scouts or an athletic team) or taking away something they care about (like a pet) because of poor marks is both unfair and ineffective. Being part of a team is also good for motivation. 

Call your child's teacher for a conference if your child's schoolwork and grades do not improve within 2 months, or if you think your child has a learning problem that makes school difficult.

If your child is struggling with one specific subject, talk to the teacher.  If the pace of work is too hard, perhaps tutoring may be in order.  Extra time spent with the teacher after class may be helpful.  Some schools have special tutoring sessions after school. If you can afford it, private tutoring from a teacher or college student may be helpful.  You can inquire with your child's teacher. or principal, or ask local colleges to put you in touch with such people.