That’s unfortunately not an easy task.
I can only speak from a German perspective here.
One way it is done in Germany is that people from OSM usually participate in one of the ’ Long nights of science’. It’s a pretty good format because you are usually interacting in a university but also general public setting.
Schools can be more tricky. Here teachers can/have to participate in upskilling seminars. One could offer one for OpenStreetMap but people would also have to choose it. Or one could offer it as an after-school activity for students.
Unfortunately it’s only one half of the problem.
The other part is that IT systems in those big systems often are very inflexible. Even if you get the interest of teachers, you’d need to convince IT department to offer the necessary tools. In the case of OSM the browser might be sufficient but even then some schools heavily restrict which websites can be accessed.
I think on of the best things to do is beeing present at events that fit your target group (web developers).
When it comes to the educational system unfortunately it often comes down to the preferences of individual educators. Some might be more inclined/in favor of open source/open data and others and therfore shape what things students get exposed to.