Our school runs Debian-Edu / Skolelinux. A central server houses the user accounts of all members of the school. We have several thin-client servers facilitating the re-use of older hardware. Then there are regular workstation installs, including on a class set of netbooks. In total we have one computer for every two students, and one for every staff member. 90 percent of these computers are running Debian-Edu.
We chose Debian-Edu for its pre-configuration of all services, and focus on software for schools. Debian allows us to spend our IT budget on hardware alone.