Review subtraction of 2 numbers whose sums would be 18 or less
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.
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.
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.