Teaching Mathematics: What, When and Why

This is a site dedicated to discussion of the teaching of mathematics: what should be taught, how, to whom, when, and why. All types and levels of mathematics may be considered, although given the interest of the current correspondents, the emphasis will probably fall on school subjects. Given such a wide domain, I intend to restrict discussion to one topic or theme at a time. Anyone may suggest a topic; if we have a backlog of suggestions I will try to arrange some voting on which is next.

We all have contact with this strange beast called mathematics. Please feel welcome to submit your ideas, your experiences learning or teaching, your hates and loves. Passion is welcome; passion with sound argument doubly so.