If your child is struggling with a particular subject area, or with homework completion in general, a tutor might be able to help. Ask your school for a list of tutors they recommend. Not all tutors are expensive. Your local high school's National Honor Society should provide free tutors. Or, offer to trade tutoring with another parent.
Be careful of large tutoring chains because they do not always concentrate specifically on your child's homework, but often provide additional curriculum and enrichment. For kids who are already struggling in school, additional work can be overwhelming and frustrating.