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.
When a child learns to relate math to everyday questions, he will be great at it from the simplest addition all the way to trigonometry. To convert percentages, decimals and fractions is thus one essential skill.
Thus, the math worksheets which you get for your kids should include interesting word problems that help them with the practical application of the lessons they learn. It should also present the same problem in a variety of ways to ensure that a child's grasp of a subject is deeper and comprehensive.
For this reason, attractive, well-illustrated worksheets with something to do will make learning fun for them. What's more, completing your worksheet will give the child a tremendous sense of fulfillment.