A frog sits on a rock at the start, and a lily flower marks home at the bottom of the pond. In between are nineteen lily pads, each with a subtraction problem, and the child colors every pad that equals 3 to make a path for the frog.
Because only one answer matters, a child has to solve every problem and then decide whether it belongs, which is more thinking than filling in boxes. 4 − 1, 6 − 3 and 3 − 0 all turn out to be the same, and noticing that is a small step toward seeing how numbers relate.
If the colored pads do not join up into a path, one of them is wrong, so the page checks itself.