I think Scheme might come out top here.Depends what you are trying to teach. If you're trying to teach computer science and programming fundamentals, then sure. If you're trying to teach people how to get 'real work' done quickly and efficiently then Scheme will only get in the way and slow people down.
For example when I've taught programming, one of the tasks I taught fairly beginner programmers was to grab some satellite images between certain dates, try to detect if there is a forest fire, measure the spread of the fire and plot the spread on a map.
With python (and its excellent libraries) this is quite quick and easy, and most people are up and running and hacking around with their programs in pretty short order. They find it really cool and inspiring and makes them quickly realise that programming could be something useful in their day to day job. Trying to start with chapter 1 of SICP and Scheme and working up from there to solving the above problem would probably lead to most of these people giving up on programming very quickly. That being said the few people that made it all the way through that would no doubt be much much better programmers because of it.