This article presents the author's response to the article "Taking Stock: Existing Resources for Assessing a New Vision of Science Learning" by Alonzo and Ke (this issue), which identifies numerous challenges that the Next Generation Science Standards (NGSS) pose for large-scale assessment. Jill Werthem comments that among those challenges is how to create assessments that reflect the vision of science literacy outlined in the Framework. She writes that Alonzo and Ke identify the following challenge as the most salient for assessment: "The Framework emphasizes that learning about science and engineering involves integration of the knowledge of scientific explanations (i.e., content knowledge) and the practices needed to engage in scientific inquiry and engineering design. (NRC, 2012, p. 11). Wertheim responds that while addressing this point, Alonzo and Ke raise important questions about the recommendation made in the 2014 National Research Council (NRC) report that items developed for NGSS might comprise sets of questions, each of which measures a single dimension of a three-dimensional performance expectation. Although unidimensionality has long been standard practice for high-quality assessment, the NGSS is pushing this standard to change for state science assessment (Gorin & Mislevy, 2013). Wertheim remarks that If assessments are to serve the purpose of monitoring progress toward the vision of science literacy outlined above, they must provide the kind of information that teachers and students need to guide improvement toward those goals (Black and Wiliam, 1998; NRC, 2001).