Siegler uses the metaphor of the wave, as in overlapping strategies for processing information.
Case uses a more traditional approach of stages.
No doubt, there is merit in both approaches and both have been show to have at least some validity. Bibliography lists 6 sources. This paper defines elements like the progression of motor structures, the development of cognition, and the progression of evolutionary elements. Bibliography lists 5 sources. The ability to assess a problem and formulate solutions has been a subject within such varied disciplines as mathematics, psychology, linguistics, neurobiology and computer science.