If Amelia Bedelia was running out of ways to muck up the Rogers' household, she has a whole new forum here when the principal mistakes her for the new teacher and puts her in charge of a class. Following the lesson plan, she begins by calling the roll (""hey, roll!""); later the class plants light bulbs for science, practices their play (jump rope and other play), and, when the reading book says ""run run run,"" they do--for Amelia Bedelia, whose books are cook books, the idea is to follow their instructions. The kids love it, especially when arithmetic turns into a free-for-all in the Rogers' backyard orchard (""Ginny has four apples, Paul takes two away"") and ends with taffy apples all round. Up to grade.