I currently have a small set of netbooks with Ubuntu Netbook Remix (download) installed that I use for various projects. If I were to set up a classroom netbook/laptop cart for a K-12 class or a school-wide 1-to-1 netbook/laptop program, I would follow what Jim Klein did as part of the SWATTEC program at the Saugus Union School District. They also used Ubuntu Netbook Remix, but with nice extras like a nice 10 second recovery system (by keeping system files in a read-only partition using UnionFS) and battery-life optimizations. The philosophy is, instead of locking down the machine, make it easy to recover from any mistakes (even the teacher can recover a netbook without needing tech support).
Karl Fisch blogged about how he implemented a variation on Jim’s program.
By the way, if you are in the market for school netbooks, or suffering from iPad envy, you might check out the $500 Eee PC T101MT touchscreen netbook, described in this liliputing post. It’s been reported to work perfectly fine with the latest version of Ubuntu (10.04, Lucid Lynx, due out later this April). Students can draw notes and pictures on the device (with a stylus), plus it has USB ports and a webcam, unlike the iPad.