They can _choose_ to use whatever they want, as long as the school doesn't force them to use proprietary stuff. It is responsibility of the school system to create an ethical learning environment and not to promote proprietary service providers. Gmail probably doesn't finance schools in Denmark either, so even less of a reason for schools there to do no-cost promotion of Gmail. And that is just one example.
Edit: After choosing something different than the school suggests, the pupils then themselves become responsible for making sure it is a suitable alternative to the non-proprietary ethical solution, that the school suggested.
Edit: After choosing something different than the school suggests, the pupils then themselves become responsible for making sure it is a suitable alternative to the non-proprietary ethical solution, that the school suggested.