Schools should be the first place where proprietary software should be replaced with FOSS.
Microsoft understands the “get them while they are young” method very well, understands that it is a very significant element of the cycle that keeps them in power, and therefore puts a lot of effort into making sure that this does not change.
So getting children to learn on FOSS and the concepts around it would result in very significant changes, especially in long-term.

Is there any project or organisation that is already trying to achieve that?
If yes, then it would be good to spread the word about them around the internet.