The Gateway to Educational Materials
An excellent resource for any teaching, but especially K-12, can be found at the Gateway, a site run by the U.S. Department of Education and Syracuse University. The site is the project of a consortium whose member institutions join what is known as GEM, the Gateway to Educational Materials.
The Gateway is an essential site, both for educators, and for anyone interested in anyone learning any topic on-line.
You will use the Gateway primarily for its very sophisticated search engine, specifically designed to search for educational materials. When you search for a particular topic, e.g. "fractals", you will get a nice listing of hits that describe not only online educational fractal resources, but also a categorization scheme linked to the appropriate educational setting. This is implemented on-screen by a category list that appears in a right-hand pane following a search. Similar to clusty, the categories allow you to instantly narrow your search into one of the categories. The categorization is an incredibly helpful way of finding the right resource for you class. For example, back to the fractal search: categories include areas such as curriculum support, lesson plans, and individual categories for grades 1 through 12.
The real benefit of the categorization scheme, however, are the categories that you probably aren't aware exist - these are the ones that allow the cross-connections across all disciplines to become evident. One of the categories that appear when searching for "fractals" is Cultural Perspectives on Mathematics. A click here yields 5 hits, one of which is African fractals: modern computing and indigenous design, an article on a fractal geometric view of the " self-organized location of huts in Tanzania, art design among the Mangbetu in central Africa, and Mali windscreens."
So plan to spend plenty of time on the Gateway - learning, teaching, and marveling at the sophistication and power of a search engines designed specifically for the educational community.