The explanations are very limited compared to actual maths lessons, though: in my experience they were very often something like "it turns out that the formula for this is...".

IMO it's scaffolded and explained a bit more than an average mathematics lesson, though teachers vary a lot.

There's a whole lot of "here's the formula" and not so much "here's the derivation" in most classrooms.

The math classes that I taught: I tried to do a lot more of the why, either rigorously or using proof by gesticulation. But there were still absolutely times that I just handed something over and was like "do this, for now."