The best reason I can think of why it sounds strange is because the word is indefinite in size. Saying a homework contradicts its nature of being indefinite by assigning a size to something that is arbitrary. For example, you can say that I have seven assignments, but I cannot say that I have seven homeworks.
Once you have identified the root of the problem, you can guide your child to a solution. 1) Find Out How Much Time Your Child Should Be Spending on Homework While there are no set rules on exactly how much homework a child should have, there are some guidelines to help you decide if the amount of homework is too much or just right.