All very good reasons to use Scala for teaching. I think you will also find that those students who really get it will sink there teeth in deep and not hit the bottom of the language any time soon. Thats good for those kids in the class who are comming into the university with programming experience. I know when I was doing my introductory programming classes I spent more time trying to figure out neat things I could do with C++ and Java then actually working on class work.