As context, here's an early paper describing the motivation behind the first edition, and why it chose a different approach from the famous Structure and Interpretation of Computer Programs:

Felleisen, M., Findler, R. B., Flatt, M., & Krishnamurthi, S. (2004). The structure and interpretation of the computer science curriculum. Journal of Functional Programming, 14(4), 365–378.

http://www.ccs.neu.edu/racket/pubs/jfp2004-fffk.pdf

A key paragraph:

> Over the past few years, we have developed an alternative approach to teaching the first course. We have translated the approach into a new text book, and we believe that it addresses SICP’s failings along four dimensions. First, the book discusses explicitly how programs should be constructed. Second, to tame the complexity of programming, it defines a series of teaching languages based on Scheme that represent five distinct knowledge levels through which students pass during their first course. The levels correspond to the complexity of data definitions that the program design guidelines use. Third, the book uses exercises to reinforce the explicit guidelines on program design; few, if any, exercises are designed for the sake of domain knowledge. Finally, the book uses more accessible forms of domain knowledge than SICP.