Could we have a discussion of when we feel this tag ought to be used?

My feelings are that mathematics-education is a highly appropriate and useful tag, but it seems at the moment to be rampantly overused. As I commented on another post recently, often m-e tends to get used as a catch-all tag when people can't be bothered to suss out a more appropriate tag (or, occasionally, when there is no appropriate tag because the question is not appropriate).

If you interpet m-e widely enough, you could plausibly put it on almost any MO question: indeed, a reasonable summary of MO is "a site where mathematicians educate other mathematicians". But this is not useful for tagging. I think m-e should be reserved for questions with explicit and significant pedagogical content (in plainer language, they ought to include "teaching" and/or "students" in an integral way).

Question types which I think deserve m-e tags include: inquiries about the Moore method, teaching evaluations, answering students' questions, is it more effective to lecture, and so forth.

Question types which I think should not be tagged with m-e include: how should I think about topic X, I am trying to learn about topic X / please suggest introductory readings for topic X, and so forth.

There is another fairly common use of the mathematics-education tag which falls between the two examples given above: the questioner asks a conventional math question, but wishes to make clear that they are looking for an answer with certain pedagogical features (ideally, that are enumerated in the question itself). Although not what a traditionalist would call "math education", this seems like a positive use of the tag.

The outcome of the meta discussion on my original question was that the question was borderline. And the poster of this new question you refer to, referred to mine for similarities.

So I suppose, mine was taken while it was borderline, and moreover I was too ignorant about the site then, and this newcomer's question was stopped because this was already decided then, as a result of the discussion on my question?

@hanche.

learning-mathematics <===> mathematics-learning <===> mathematics-education.

What's the difference?

What Hanche says is exactly the point I was trying to make! In my opinion we should not use [and even retag] math-education in the situation "I'm trying to learn math" and especially not in the situation "I am trying to learn math topic X" (i.e., when the primary content of the answer is mathematical content).

Harry is right that math education is a separate major or program in (to speak of what I know) many US universities. In fact, my own University of Georgia has the number one math education program in the country. (A couple of years ago I was flipping through the Notices and found a table of universities at which UGA was right at the top. At first I thought "Wow, as fantasy dreams go, this one is pretty tame" and then I noticed that the article was about math education.)

I think that on our site it is inevitable (and to me at least, desirable) that the m-e questions are still going to have some mathematical content. E.g., imagine the question "Which courses are especially well suited for the Moore Method? Badly suited?" A math educator who has not done research on this specifically may not be as helpful as a thoughtful research mathematician who would tell you, for instance, that General Topology is a sensible as well as a popular choice and Differential Geometry could be a disaster ("Write down the Christoffel symbols. No, that's not right. No, that's not right either...[two weeks pass]...OK, I'll give you a hint: there are three indices...")