Worksheets also, when used properly, provide both the students and parent / tutor immediate feedback as to the child's progress. This means they can be used to point out areas where the student needs further reinforcement.
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.
When you're teaching your student to write, there are a whole host of worksheets online that you can use. Many of these include clipart that will help the students learn the sounds of letters and letter combinations. There are other sheets that help the student learn to write his or her numbers. It's helpful having printable worksheets for something like this, because parents often go through quite a few of these before the child masters writing the numbers or letters correctly.
Hopefully this has inspired you to develop exciting and engaging review worksheets for your class when needed and your students achieve as much as they can when it comes time to test.