Common Core State Standards for Mathematics (CCSSM) is different from the objectives that many teachers have previously experienced in their state frameworks. Although the mathematical topics of the two may be the same, the mathematical expectations within the Standards require a deeper understanding by teachers and students. In this article, the authors demonstrate how using the ideas of "Understanding by Design" (Wiggins and McTighe 2005) can support third- and fourth-grade teachers in "unpacking" a Standard and, in turn, clarify the expectations of a Standard and the end goal of instruction. Supporting students in meeting the expectations of both the Mathematical Practices and Content Standards also includes task selection, task implementation, and instructional decisions based on informal assessments. By unpacking Standard 3.NF.1 and examining a sample task, the authors have proposed a means for teachers to think about these processes and navigate through the CCSSM document. With the support of their colleagues and the insights shared here, teachers too can better understand and implement the Common Core. (Contains 8 figures.)