My undergrad intro class used this. At the time I found it patronizing and silly and artificially limiting, having coded before (the design recipe, the different "levels" of scheme).

But I saw some of the wisdom in the approach when I later tutored the class. People would try to rush into coding problems without doing real analysis of what the cases would be, and had a foggy notion of different parts of program having a "contract". HTDP and the design recipe makes that muscle memory for beginners which is pretty nifty.