The teacher's experience and the sequence of skills in the students' basic math program are the best guides in determining which skills should be introduced first. In general, the scope and sequence chart above can be used as a guide.
A number of sets for younger children are "color coded." Some teachers present all the levels with an exercise set, while others prefer to present all the blue (two-digit) exercises, progress to the pink (three-digit), and culminate with the green (four-digit).
Other skills such as Roman Numerals require no prerequisites other rhan an understanding of place value. Such exercises can be presented any time.