'Learning Progressions' are a relatively recent approach that describe the progression that can be expected of learners through their education. A Learning Progressions framework can also be used to support teaching and learning, assessment, and curriculum design. To benefit teaching and learning, a Learning Progressions approach aims to provide detailed instruction on the optimal order for presenting material within a subject. To support assessment, a Learning Progressions approach aims to provide a framework for comparing different learners in order for the results of such comparisons to be useful for learners. To support curriculum design, a Learning Progressions approach aims to provide a method of refining the material presented to learners. This article outlines the specific theory of learning that underpins the Learning Progressions approach, and then explores a series of simplifications that are inherent to it, to evaluate the suitability of the Learning Progressions approach for supporting the design aims outlined above.