These charming books approach their subjects with good humor. For example, in Subtraction, Sebastian and his friends are on a camping trip where various items are being pilfered by some mischievous mice. While the bewildered campers use subtraction to figure out how many of their belongings are missing, the inventive rodents use the purloined hot dogs as water skis and the paddles from the friends' boat as a diving board. These titles will have children laughing as they learn the concepts that are clearly demonstrated in the story line. Each one includes a practice section. With their sunny watercolors and engaging characters, these books will be welcome additions., School Library Journal April 2009.