Many schools in the US have been using Chromebooks in the classroom for some time because they have been a less costly alternative to Microsoft and Apple products while also offering a secure and simple way of introducing students to the real world of computer learning. This early exposure to Chrome OS is partially responsible for the increased adoption of Chromebooks for use in the home and elsewhere. My 11 year old granddaughter has had her own Chromebook for a few years and she can connect to her school network at any time. As she likes to say: "it's self-explanatory".
The other reason that schools have gravitated toward Chrome OS is because their older computers that are no longer powerful enough for Windows can be loaded with Chrome OS and given new life.
I think most of them are using the version provided by Neverware.
Excellent point. And for some old pcs, and new ones, Chome OS or Chromium OS can be run on then with just a usb flash drive. $$ saved.