The concept of "learning progressions" has begun to show up in discussions of education policy and research as a potential answer to the question of how to specify what being "on track" might mean. A number of recent NRC (National Research Council) reports on science education highlight the concept (National Research Council, 2001; National Research Council, 2007). The National Science Foundation (NSF) is funding quite a bit of research and development on progressions in science and mathematics. Mathematics education researchers tend to use the term "learning trajectories," or "hypothetical learning trajectories," for an essentially equivalent concept. Some national education systems, and some of the Australian states, use the term in describing the levels of learning in their common curricula. As noted above, the idea informed the development of the Common Core Standards and turns up as well in the language of the two Common Core state assessment consortia. In the past three years, with support from Pearson Education and the William and Flora Hewlett Foundation, the Center on Continuous Instructional Improvement (CCII) organized two working groups of scholars and education researchers to review the concepts of learning progressions and learning trajectories as they are being applied in science and mathematics education; their purpose was to try to clarify what they are and what is known about them, and to assess their potential usefulness for informing the development of better standards, curricula, and assessments. As a result of these deliberations, CCII produced two reports, one for science and one for mathematics (Corcoran, Mosher, & Rogat, 2009; Daro, Mosher, & Corcoran, 2011). This policy brief reviews their conclusions and the implications of their findings for policy and for future research and development. (Contains 1 table and 2 footnotes.)