Informative math website by Cynthia Lanius. One of these is the dueling pinwheels lesson for Geometer's Sketchpad. The Hand Squeeze is a data collection and analysis activity.
Look at the quadrilaterals lesson in the geometry located near the upper left corner. Check out the numerous other interesting lessons and links on the site.
Problems "with a Point" help students in grades 6-12 learn new mathematical ideas by building on old ones. Each problem or sequence focuses on one mathematical idea and also connects that idea with others.
National Council of Teachers of Mathematics. See Principles and standards for school mathematics, as well as the Navigations and the on-line Illuminations.