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.
They're also available for nearly all grade levels. There are printable middle school, high school, elementary school, and even pre-school worksheets.
Ratios and proportions are likewise wonderful math lessons with plenty of interesting practical applications. If three pans of pizza, one kilo of spaghetti, two buckets of chicken can properly feed 20 hungry friends, then how much pizza, spaghetti and chicken does mom need to prepare for birthday party with 30 kids?
Review subtraction of 2 numbers whose sums would be 18 or less