Tracking Web Site Changes and Lost Web Sites
With the advent of RSS, page change detection sites disappeared for a while. However, new technology has revived and refined the concept. Web sites like these can help you keep monitor web sites and locate "lost" web sites.

Free Tools to Monitor Website Changes
If you want to know if a website has updated its content, you can just go to the website and check it manually. This gets old when you have multiple sites or pages you'd like to keep track of. Enter web content monitoring tools. They monitor changes on any website you're interested in and send you an alert or email.
This post identifies 5 content monitoring tools that notify you of any changes in your favorite pages without having to constantly check them yourself. The services are usually free if you are only checking a few pages.

Visualping
Visualping is an exemplar of the current web page tracking tools. Rather than flagging any change in the entire page – which can contain ads, the current time, etc. – you can select what part of the page you want to be monitored. The service will check the page (usually daily or weekly for free accounts) and email you when things have changed.
Different monitoring sites have different options. Try out different offerings to see which one works the best for you.
Tools like Visualping can be used to monitor student maintained web sites. Get a heads up as soon as new content is posted.

Internet Archive
Internet Archive, a.k.a. the Wayback Machine, archives literally tens of thousands of sites on the Internet, tracking changes in the site's content over time. You can use it to find a lost article or web page, or to see how your favorite web site has evolved over time.
Use the Internet Archive as a teaching tool
Compare older and newer versions of a web site to show how attitudes -- and web styles -- have changed over the years.
Where did they go?
We use the Internet Archive to locate web sites that have moved.
- Find the last good version of the web page in the Archive.org and copy 8-15 words of text from the page
- Go to Google and do a search for these words, surrounded by quotes.
Many times we've been able to locate "lost" web sites using this procedure.
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● Office 365 For Education
● Evaluating the Quality of Information
● Computers in the Classroom
● Algodoo 2-D Physics Sandbox
● Audio/Video Primary Sources
● WebQuests And Scavenger Hunts