In other words, they never memorized their multiplication tables! Many times I have seen a student do poorly due to a weakness in basic math facts they should have learned in third grade.
Another important point I keep in mind is that I never want this regular math review time to take up and hour of class time. I want it to be quick but effective. This is not instructional time, but time for the students to review material they have already learned.
How many kids in school have done their homework? Again this can be answered in several ways: in percentages, 70%; or in ratio, 7:10; Both of these mean out of ten kids in class there are seven good ones who did and three not-so-good ones who didn't. The bottom line is that kids learn math much better when it makes sense.
They're also available for nearly all grade levels. There are printable middle school, high school, elementary school, and even pre-school worksheets.