Researchers in the areas of psychology and education strive to understand the intersections among validity, educational measurement, and cognitive theory. Guided by a mixed model conceptual framework, this study investigates how respondents' opinions inform the validation argument. Validity evidence for a science assessment was collected through traditional paper-and-pencil tests, surveys, and think-aloud and exit interviews of fifth- and sixth-grade students. Item response theory analyses supplied technical descriptions of evidence investigating the internal structure. Surveys provided information regarding perceived item difficulty and fairness. Think-aloud and exit interviews provided context and response processes information to clarify and explain issues. This research demonstrates how quantitative and qualitative data can be used in concert to inform the validation process and highlights the use of think-aloud interviews as an explanatory tool. (Contains 4 figures.)