Evaluators must employ research designs that generate compelling evidence related to the worth or value of programs, of which assessment data often play a critical role. This article focuses on assessment design in the context of evaluation. It describes the process of using the Framework for K-12 Science Education and Next Generation Science Standards (NGSS) to design assessments to evaluate the efficacy of a curricular intervention. The new science standards present a significant challenge to assessment designers and evaluators because these standards emphasize the integration of disciplinary core ideas, practices, and crosscutting concepts. This article presents the structure of a validity argument for such uses with an evidence-centered design perspective and unpacks the design decisions in developing and implementing these assessments in an efficacy study of a project-based science curriculum. Implications for designing NGSS-aligned assessments for program evaluation purposes are discussed.