Don't assume the entire burden of helping your child pass this year. Schools have many professionals that can help you. Contact the school psychologist, school social worker, guidance counselor, principal, or a school problem-solving or intervention team. Not only will these people have ideas for you, they will also have suggestions for your child's teachers. Furthermore, they can initiate testing to find out why your son continues to have problems in school. And they can place your child in tutoring, counseling, and special before- and after-school remedial programs that could definitely make a difference for your son.
For the rest of the school year, your son needs to spend at least one hour each day at home on his schoolwork. This work should be done in an area where you can observe him. If he doesn't have homework every night, ask his teachers for alternative assignments that he needs to complete to improve his grades. As far as helping him with homework, try to limit your assistance to making sure that he understands the assignments.
Start next year out right by expecting your son to spend at least one hour a day on his homework from the first day of school. Also, you should request a weekly report on his grades so you will know how he's handling his classes and whether or not he needs special help early in the year.