[star] The Last Marshmallow [Storytelling Math] by Grace Lin; illus. by the author Preschool Charlesbridge 16 pp. g [star] Up to My Knees! [Storytelling Math] by Grace Lin; illus. by the author Preschool Charlesbridge 16 pp. g [star] What Will Fit? [Storytelling Math] by Grace Lin; illus. by the author Preschool Charlesbridge 16 pp. g In board book form, Lin accomplishes that most difficult of tasks: creating engaging, accessible, age-level-appropriate, not-too-fussily illustrated stories that also teach something. In this case it's math. Each entry homes in on a specific mathematical concept, while together providing a tour through the seasons -- and a slice-of-life portrait of three friends, Olivia, Mei, and Manny. In the springtime-set Knees, Mei observes measurement and comparison as she cultivates a sunflower. Circle! Sphere! proves the mind-stretching fact that the children's three different-shaped bubble wands produce the same-shaped bubble. Fit's setting is a fall farmers' market and illustrates Olivia's spatial sense (and taste in produce). Wintry Marshmallow touches on division, both mathematical (how to split three marshmallows between two girls...) and behavioral (...without ruining the friendship). The illustrations are signature Lin -- think The Ugly Vegetables (rev. 9/99) and the Ling and Ting books -- with bold, saturated hues; thick black outlines; judicious use of frames; eye-pleasingly tidy details; and nothing extraneous. Brief "Exploring the Math" notes and "Try This!" suggestions, addressed to adults and written by an early math expert, are appended. All together, these diminutive math storybooks add up to a whole lot of fun. Elissa Gershowitz