In this article, the authors provide their critique on a set of papers that investigated Mathematics Knowledge for Teachers (MKT) assessment and the underlying theory and characteristics of the validity enterprise. Three types of assumptions and inferences--elemental, structural, and ecological--are discussed in these papers. These assumptions provide a general and prescriptive validity framework that will enable assessment developers to plan comprehensive validity investigations that incorporate appropriate types of evidence gathering: psychometric and statistical, qualitative, and experimental. Here, the authors opine that the prescriptive three-facet approach mapped out in the papers that incorporates sophisticated psychometric methods and is strongly interdisciplinary, adds significantly to this work by offering a solid and practical contribution to the theory and methods of assessment validity, and by providing an important concrete case example.