The Multiplicative Reasoning Assessment (MRA) includes items with atypical representations of mathematics to assess the multiplicative reasoning of elementary-aged children. However, peer review on the use of such non-canonical representations for assessment items has received critique. A recurring question in many scholars’ reviews is, how one can be certain MRA items, which incorporate an unconventional item design, are a valid means for assessing multiplication and division, rather than using canonical formats including expressions, equations, or word problems? The chapter focuses on this question by presenting and examining evidence of content and response process validity collected over the past several years for the MRA.