[dragonwriter]

The Pyret style much more closely follows the abstract (divorces from any particular PL) analytical, contract-based problem solving approach taught as central to programming and as properly preceding actually writing code in, e.g. How to Design Programs (which uses Racket as the concrete programming language.)

So, for a curriculum based on that basic approach that starts with the analytical methods and then adds concrete programming on top of it, the Pyret approach -- which requires and gives effect to elements of the analytical product that Python would not require and provides no convenient means to clean express that also gives it concrete effect -- is probably both simpler (as the two-way correspondence between code and analysis is better) and more productive.

It's probably not particularly useful to discuss the quality of a pedagogically-focussed language outside of the context of an approach to pedagogy.