scolding [a student] for using ideas that weren't being taught in his classroom.?

Very common!

Pretty common (in North America anyways) I think. In speaking with teacher friends my impression is that math education has become quite formulaic with a large focus on learning algorithms to solve problems that occur in standardised tests.

I happen to be in 10th grade in the USA and really love math - and using it to solve applied problems - but the math taught in school is formulaic and mechanical. We aren't encouraged when we start asking questions not covered by the curriculum or congratulated when we answer them ourselves.

It would be really nice if we had more teachers like the one in this article. I'm sure many more articles would be written then.