I tried teaching some Codea to a high school programming class, where the teacher had finished the course material very early and was looking for something to engage them. They had been doing some kind of accounting project using VB6 (!) until then.
I prepared several step by step projects, starting with just one Lua lesson (far too little, I know, but I have brought up teenagers myself so I know their attention span) and one on physics, games etc.
It didn’t work at all. It was a total flop.
Some of the kids were not interested at all in anything that looked like work, and just played games on the iPads.
Some of the iPads played up, because they were shared library iPads, so I wasted ten minutes every time, just on that.
The kids who were interested in programming looked briefly at what I had prepared and then went off in all directions trying to do things, which just resulted in questions I didn’t have time to answer.
Now I fully realise that I wasn’t a professional teacher, and the kids only had iPads in class, and that the class teacher had not done a good job of making them realise that even fun programming languages require some preliminary hard work. (On this forum, too, we see a lot of young people arrive with fond dreams of having the next Flappy Birds up on the App Store by next week…).
I came to the conclusion that while Codea is one of the simplest languages around, and one of the most exciting in terms of what it can do, it doesn’t teach itself, and still needs to be taught in the context of a CS class by teachers who knows how to teach programming to teenagers.
Having said that, there are, I believe, some teachers who have taught with Codea. Try googling on the forum and elsewhere.