I've contemplated teaching level design at some point when I retire.
There's a lot to it, and often it seems that only the most basic aspects are emphasized, like architecture and overall look and design, rather than things like playtesting theory, statistical analysis, etc, etc.
More or less, most people can design a pretty looking level. Well, anyone who's any good at level design, anyway... But designing a level that plays well is a much harder task and I get the feeling that a lot of people don't understand what makes a better playing level and what doesn't, or how to time FPS levels so that both sides meet in the middle, and things like 'how to build a good choke point'.
I suppose a lot of this knowledge comes from personal experience, and it's hard to give these sorts of things to other people in tutorials, because you have no idea how to tailor it for every person that reads it, and what their individual level of knowledge is. I suppose that by the time I retire, there will be universities with game development programs large enough to actually need a teacher that would cover something this specific. I hope, anyway, heh.