The content is correct, unique and original. Ideas and images are properly cited with respect to copyright laws. The format is well organized and skillfully designed for ease of use. There are obvious connections between the content of the web page and some type of curriculum standards. The pages have a clear purpose and audience in mind.
Visitors can learn from the pages.
If they are used, they should be integrated seamlessly. They should not distract from the main content and they should be not used in excess.