Teacher: "The corner is the best place to make territory. Here, Black makes six points of territory.
Pupil plays his first 6 moves as shown by his teacher
Teacher: Well, actually, this is too slow. You should invest stones in open areas first.
Pupil becomes a little confused. Next he ignores weak groups to play loose stones in open areas .
Teacher: "Well, you have to defend weak stones."
Pupil: "How do I know when my stones are weak ?"
Teacher: "When they will be captured if you neglect them."
Pupil: "How do I know when my stones will be captured"
Heh, #:-7, serving my argument, of course. But the pitfalls of explaining territory are manifold. See also Don't use thickness to make territory, another persistent flaw in even experienced players' games and give up some territory, one of the worst fears keeping people from playing decent Go.
A straw-man that stuffed is a fire hazard.
A more likely scenario:
Teacher: "The corner is the easiest place to make territory as you only have to enclose two borders. Next easiest are sides of the board with three borders, and the center is hardest because you would have to make four borders. You want to surround as much territory using as few stones/moves as possible.
Pupil plays his first 6 moves as in the diagram above.
Teacher: "Well, that would enclose an area, certainly, but you've expended many stones inefficiently and meanwhile let white make several loose claims on all the other easy parts of the board. Go is a game the emphasises balance, and you chose one extreme -- firm and absolute claim over an area -- and you would lose the game because of it. The other extreme, of scattering stones indiscriminately and not defending where necessary would also lose the game. That balance is hard to find, but you will learn to find it over your first hundred games or so."
Bad teachers can screw up any method and the teacher in my example probably does a poor job explaining territory. Using capture go the wrong way indeed leads to confusion as well. The fundamental difference, in my opinion, between capture and territory is that the latter (and efficiency, balance and claim) is not a basic concept. You need some experience to understand what territory is. You can't get any experience without knowing how to capture. That's why I prefer a good teaching job using capture go, above a good teaching job using territory.
See capture go discussion for a lot of interesting arguments pro and contra.
I don't believe exactly in Capture Go either, ultimately I have to at least mention some vague idea of territory if I teach introductory Go. Otherwise, I can babble non-stop on the various capturing techniques to be stopped and asked, "What is the objective of this game?" And it happens every single time I fail to mention the idea of territory. Still, I will focus on some basic capturing techniques in the first introductory lesson.