Northwest Evaluation Association™ (NWEA™) conducts norming studies every several years to provide the best and most up-to-date information we can about student achievement and growth to better support educational decision-making. It is an important part of our commitment to our partners. The most recent NWEA norms were released in July 2015. Just as we expect student performance to change with time, norms of student performance will change correspondingly. For 2015, several factors may have influenced how the US school-age population performed on Measures of Academic Progress® (MAP®) assessments of language usage, mathematics, and reading over the 2011-12, 2012-13, and 2013-14 school years. Prominent among these possible factors are the introduction of Common Core instruction and Common Core versions of MAP. But as with all empirical studies, changes in scope and data necessitated changes in statistical design and analyses. The methodological improvements introduced in the 2015 norms have resulted in a set of norms that are more representative of the US school-age population than previous NWEA norms. Methodological changes involved differences in the way post-stratification weights were developed and the way growth was modeled. Details of these changes are addressed more thoroughly in the 2015 Norms Study. As a result of the improved methodology, partners can expect some differences from previous norms, as explained below.