Tek Mom has assembled a good assortment of search tools and data bases for the younger audience. Visit  www.tekmom.com

Here is another great site for students.  There are many search tools on one page.  Go to  www.ivyjoy.com/rayne/kidssearch.html

This one is from the National Council of Teachers of Math. There are many math activities for all grade levels.
http://illuminations.nctm.org/

Students have enjoyed making virtual snowflakes. It's fun, and a great way for youngsters to improve their mouse navigational skills.
http://snowflakes.lookandfeel.com/

Enjoy a huge assortment of printable and interactive maps - and more.
http://nationalatlas.gov

Another government published site, the World Factbook, is full of information about countries of the world.
https://www.cia.gov/library/publications/the-world-factbook/index.html