It always surprises me when some people who rely on computers for their livelihood lack even the most rudimentary idea of how they work. For many, they don’t feel they need to know more than, “I press this magic button and up pops the Google. Other folks, however, are more curious. For them, the folks at Gizmodo have sent up a series of lessons and videos to teach the basics of what is going on inside a computer and its separate components that makes it do what it does.
Now the lessons and videos are free to access, but if you want to actually do the hands-on part and recreate what you see in the videos, you need to buy a reasonably priced Electronics kit ($40). This is a great resource for teaching circuitry or an introduction to computers for middle and high school students.
A piece of advice — Gizmodo is a large blog and there many links in which to get distracted and wander off the page, so some assisted navigation is probably wise for younger students.