Maddie's birthday party and the house is a mess! Toys are everywhere, even in the bathroom. Dad helps carry heavy things up to her room, while Maddie gathers the rest. But it's up to Maddie to put everything away. As Jumbo the cat and Teenie the dog watch, she turns into "Mighty Maddie," a caped super-hero able to sort toys in a flash by how much they weigh. The fire truck is heavy, but the ballerina tutu is light, and the feather tiara is even lighter. Sometimes things that are big, such as pillows, are lighter than things that are small, such as books. Will Maddie manage to get everything stashed away neatly in time for the party?

Understanding that the weight of an object is not always dependent on size—mass—is an important measurement.