Many children tend to be impulsive and have trouble planning ahead, keeping up with long-term projects, making thoughtful decisions, and turning in all of their homework. These abilities are all a part of executive functioning. (See Executive Functioning: How It Affects a Student in School.) Most of the thought processes involved take place in the prefrontal cortex which is the part of the brain just behind the forehead. This part of the brain is not fully formed until students are out of high school, which explains why adolescents often have trouble making decisions.
Students vary in their ability to manage their day-to-day life because they do not all develop at the same rate. Nearly all students get better as they get older. If they are struggling with executive functioning in school to the point where it is affecting their success, they need additional support until they can manage their schoolwork by themselves.
If your child has trouble turning in all his homework, a good starting point for help is to set up a homework binder. This binder should be a bright color that is easily spotted in his book bag. The binder should contain the assignment sheets from each of his classes, any handouts that relate to that night’s homework, and a place for completed work to hand in the next day. As he completes the homework for each subject, he should cross it off, making it clear that assignment is finished. The completed work goes in its own section. If there is a question he cannot answer, he should highlight it so that he can ask for help with it the next day. (He needs to understand that he should finish everything else on that assignment.) The binder should also house special notes or permission slips that need attention from parents.
Your child needs help learning to use a homework binder. It will take time before she sees it as her “survival guide” to school success and using it becomes a habit. Once this organizational skill is mastered (she uses it without you reminding her), select something else to start working on. It is best to work intensely on one student skill at a time so she will not feel overwhelmed.
For a thorough discussion on executive functioning, read "What is Executive Function?" by the National Center for Learning Disabilities. They also have a free ebook with explanations and strategies for ways to help.