I guess central Europe, because what the OP says is similar to what I know. However, I don't claim it is the same country I am in, because a few things differ.
If any EU country, it means roaming isn't an issue, as there is EU wide mandatory roaming with all phone contracts.
@Elsvieta
Families who can't pay could get school assistance with the fees
@Banannanana not necessarily. The OP already said teachers only, no additional instructors. And I remember having a time for free skiing at school ski trips. And it wasn't about blue and green slopes.
In my country in my school we did local ski trip at 12 for learning basic and Alps at 14 to enjoy skiing. As Alps are relatively more expensive for us, it would be a huge waste of money to go to Alps to do the basics with instructors.
And yes, we were absolutely riding without adults.
It doesn't mean we are irresponsibly dying en mass on slopes though.
In my country students of teaching at university can take skiing, swimming and summer outdoor sports modules, so practically all PE teachers and many others have a qualification. So we, as parents and students, don't think about the qualifications at all, because it is normal that teachers do it.
The free riding can be for example one nice slope at the beginning - so the teachers are around, can observe behaviour and decide whether to extend the area.
I was in a grammar school equivalent, so I don't know how this works elsewhere, but we behaved- because being allowed to just ride in a small groups was a privilege.