Unless the build quality is stellar and/or the size makes a difference, I would much rather pick a machine from their Essential series (to keep the discussion to the same manufacturer, similar options exist). It is not tied to an ever-changing online service, it has the specs to act as a stand alone work machine for myself, let alone school students, and only costs $369.
You're suggesting giving schoolkids a 3kg 15.6" laptop? It seems clear that it's not acceptable no matter how good the specs are. A rugged 11" laptop makes way more sense.
As for ChromeOS, it seems like a perfect fit to a school environment. But the same ThinkPad model has been available for about a year with Windows.
http://www.lenovo.com/products/us/laptop/essential/g-series/...
I recently picked one up for a family member and was impressed by how much computer <$400 will get you.