Subtract 1- or 2-digit number from a 2-digit number with/without renaming
However, caution must be taken into account when review is repeatedly covered in your classroom. You do not want your students to become bored or frustrated with the repetition.
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.
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.