The National Council of Teachers of Mathematics offers this page with resources for grade school students and instructors. Mostly comprised of lesson plans broken down into four ranges of grade levels, Illuminations has single and multi-day online exercises. The investigations are presented online for teachers to review, but the interactive, multimedia activities can also be downloaded for student use. Both Windows and Macintosh operating systems are supported for these applications, and easy to use Java applets provide students with fun, educational materials that demonstrate common principles of mathematics. Over 900 external Web resources are also listed and grouped into specific categories.