> I remember being told at school, that we weren't allowed to use calculators in exams
I remember being told the same thing, but I happen to believe that it was a fantastic policy, with a lackluster explanation. The idea that you wouldn't have a calculator was obviously silly, even at the time, but underlying observation that relying on the calculator would rob you of the mental exercise the whole ordeal was supposed to be was accurate. The problem is that you can't explain to a room full of 12 year olds that math is actually beautiful and that the systems principles it imparts fundamentally shape how you view the world.
The same goes for essays. I hated writing essays, and I told myself all sort of weird copes about how I would never need to write an essay. The truth, that I've observed much later, is that structured thinking is exactly what the essay forced me to do. The essay was not a tool to asses my ability in a subject. It was a tool for me to learn. Writing the essay was part of the learning.
I think that's what a lot of this "kids don't need to calculate in their heads" misses. Being able to do the calculation was only ever part of the idea. Learning that you could learn how to do the calculation was at least as important.