In order to demonstrate the differences between search engines, use an LCD projector or have students at individual terminals do a search for a key word. Using an LCD projector or having all students do this at once helps to emphasize the difference that better searching can make.
Do a key word search using "seals" on Yahoo!
Ask them to observe and make note of the kinds of sites that were found (most of them have to do with seals and gaskets or Easter seals).
Then, do a search for "seals" on AltaVista.
Again, ask them to observe and make note of the kinds of sites that were found.
Finally, introduce them to the "narrow search" function on AltaVista.
Narrow the results for the "seals" search, and then observe and make note of the kinds of sites that were found.(The sites get progressively better.)
Then, do a search for "harbor seals."
You could also demonstrate different search techniques such as wildcard symbols.
Ask students to search their own topics, using different engines and different key words, in order to find which ones work best.
This could be done using any key word or any search engine. Note how using a more specific key word produces much better results on the first search.