Despite all of the modern games and toys available to children these days, they still find spinning objects inherently interesting. Boys and girls of all ages will spend hours, if given the chance, making and playing with tops and yo-yos. Watching a simple toy whirling on the floor or table can be delightful and engaging, and making a yo-yo do exactly what you want it to do can be very satisfying. The Spinning Toys project builds on this interest, giving children an opportunity to learn how to manipulate the materials that compose tops and yo-yos and to figure out and explain the physical principles that govern spinning things. As children work through the challenges in this Spinning Toys project, they will also learn about experimenting, testing, making observations, asking questions, and explaining what they did and why they did it-- the essential elements of critical thinking and the inquiry approach to engineering and science. In this project, children will be designing their own tops and yo-yos. The first two tops activities and the first two yo-yos activities are structured. The children are led through the beginning steps of making an effective spinning toy with a limited range of materials. The purpose of this process is to make sure that all the children have a common understanding of the principles of top or yo-yo making before they move on to the final, open-ended challenge for each toy.