Linux has an excellent selection of educational software for children and adults. Here are my observations on those titles I've had an opportunity to install and watch people use. …
Childsplay: A suite of educational games for younger children. Localized into several languages.
Gcompris: A suite of over 100 activities for ages 2 to 10. Localized into over 40 languages. Administrative module allows for customization and tracking appropriate for schools.
GRE Tools: A vocabulary building tool, consisting of a synonym quiz, a word guessing game and a word browser. It automatically remembers the words you had difficulty with and lets you revise them. Gnome/GTK.
Pysycache: Activities to teach mouse manipulation skills to children ages 4 to 7. Localized into several languages. Extensible through downloadable themes and topics available on the project website. Not yet fully tested. TODO: Does not work out of the box on Mandriva 2008.1; need to document how to set it up. See the PDF manual that comes with the package.
TuxMath: A math tutor for children in arcade game style. Appropriate for grade 1 through low junior high.
Tux Paint: A drawing program for children ages 3 to 12. Localized into several languages. Works fine on slow computers. The optional package tuxpaint-stamps adds additional images and is recommended.
TuxType: A typing tutor to reinforce typing skills in arcade game style. Does not teach typing; it provides practice for the student who has been taught the basics. For teaching the basics, Ktouch and Gtypist have been recommended. TuxType is localized into several languages. TODO: Look into difference between packages tuxtype vs. tuxtype2; I have tested the former, which works well.