100 Days Of School (32 pp.; $21.90; Sept.; 0-7613-1271-4): Readers will want to try the more interesting variations on math Harris has devised, e.g., addition and subtraction using clowns, trains, blackberry pie, and centipedes. Harris demonstrates that numbers can be broken down into recognizable units that can be manipulated and remembered: If “10 tired children all take off their shoes, what do you get? Lots of bare feet . . . and 100 toes!” Johnson’s brilliant artwork will make children forget they’re learning, complementing the whimsical text as it slyly works in the basics. A math-class must, but also at home in story hours. (Picture book. 5-8)