The problem with Scheme is that it's very difficult to learn in a vacuum. You can do all sorts of interesting things with it, but if people can't use it to do real work then they quickly lose interest (I'm not talking about CS types who are interested in computing anyway, but others who would fine programming a useful skill in their "real" jobs). From that POV the best teaching language is something like VBA, awful tho' it is, because it gets people from zero to "look what I did!" very quickly. Or MATLAB or some other language that's looked down on by purists.