I believe web design has changed significantly since Jakob Nielsen devised his guidelines. The impact of graphics is severely underrated in his opinion and design has moved from a frames based environment to tables, css, and php. As a webmaster myself that is currently undergoing a redesign, it has been interesting to see what "general consumers" of websites value as well as what they take for granted.
Usability: ADA compliance is a big issue in my book. The ability for those with disabilities to be able to get access to the same information as others is imperative, especially in a school based setting. Also, ADA guidelines just ensure good practices, by including alt tags, using headers to designate information, etc.
Navigation: It is key that users can get to the information they need. A hierarchical structure needs to be established that is consistent throughout the site. There should also be an easy way to go backwards, without having to use the back button, etc.
Design: The design needs to not get in the way of the message, but help convey it. Animated gifs, garish clashing colors, frames, all get in the way of getting to the information, they are distracting or cumbersome.
Authority: Using the google model, who links to this site and what sites do they link to. Does the site provide references or links to claims that it makes? Is it ranked in any websites such as digg, technorati, or the buzz? Are author or group credentials provided? When was the last time it was updated?
Of all of the criteria, I believe that having students understand that anyone can put information on a website, and that the fact it exists on the Internet does not mean it is correct or factual. They need to backup claims made on pages and corroborate them with either other methods of evidence, or other authorities on webpages. (On a side note: I would also like to point out that just because something is in a book does not make it authoritative either).
One issue I'd like to get more discussion on. As a general rule you should not have to scroll down a webpage to get information. Do you think that is true anymore?