For many middle-school children, math is a real challenge. It is at this age that the concepts begin to get more abstract, and work goes beyond "concrete" ideas like adding and subtracting. It's no surprise that at this age, math can become something the student avoids, or begins to dislike.
Homeschool worksheets are a vital part of the student's homeschool experience. They allow the child to test his or her knowledge, and they offer them a practical application for their learning.
As a middle-school math teacher, I have seen many students who do understand abstract concepts, and even enjoy learning about things like Pi and the Pythagorean Theorem, but who appear to be unable to do so due to a weak grasp of math fundamentals.
How much money do I have left if I buy a soda? By the end of the week, how much of my daily allowance will I be able to save if I don't?