Screen shots from the "The Number Race" rehabilitation software. a. Sample comparison screen. The child plays the character of the dolphin, and has to choose the larger of two numerosities, before her competitor (the crab) arrives at the key and steals the larger quantity. b. Another sample comparison screen, taken at a higher difficulty level on the "complexity" dimension where addition and subtraction are required to make a correct comparison. The screen shows how operations are concretized by corresponding operations on sets of objects, after one of the characters wins (in this case the competitor). c. Sample board screen. After each comparison, the child uses tokens won to move a corresponding number of squares on the game board, where she must avoid landing on hazards (here depicted by anemones). Once she arrives at the end of the board, she wins a "reward" fish to add to her collection. Winning enough of these rewards unlocks access to the next character.