If it was purely an issue of "on by default" I think it would be one thing. But because it is often, it appears, enforced as unavoidable private company data collection pushed through school policy then it becomes a much bigger issue. That means that government, albeit local government, is basically selling the right to student monitoring to a private entity that has promised not to collect that very data targeted at students contractually.
The issue when schools require Chromebooks be used in a certain way means that the students are not given the option not to be monitored. "By default" is one thing and potentially problematic on its own. But if schools are requiring that students submit to being tracked by a private company without oversight that's a much, much bigger issue.
It is a chain reaction: school is a requirement, parents and students are not given a choice about the tools that they use, tools are enabled to track students, no opt out.... students are simply required to be tracked. It's not a "direct" situation, it's big brother via a chain of circumstances and rules that result in the same thing. A serious situation needing attention for sure. Thankfully it looks like the EFF is on the case.