With the financial constraints of most public schools, they probably have to pick one of the two.
"However, that profit margin is a key component of Apple's success, allowing Apple to constantly reinvest in the brand, driving innovation and R&D across hardware, software and content development." Apple could also make cheaper laptops with plastic cases and cheaper CPUs, but making mass quantities of cheap hardware doesn't seem to be part of Apple's current strategy.
Given the choice between a $300 iPad and Chromebooks that start at $150, it'll be hard for schools to pick the former over the latter.
Sure, one has sleek and powerful apps, but the other has a keyboard, with all the important functionality, for a cheaper price.
At the end of the day, Apple has stuck to its guns as a purveyor of high-end electronics.