Also, price is a consideration. Lenovo's Windows-based X131e, for instance, starts at $539. Schools could some money by getting Chromebooks instead, and they won't have to worry about viruses or deal with installed software.
It's unclear if Lenovo plans to do more with Chromebooks in the future, but there are rumors of a Chromebook with a touch screen in development (though rumors of a late 2012 launch didn't pan out). Maybe Lenovo, with its many experiments in convertible Windows 8 machines, would be a good candidate to release one.