The purpose of this report is to describe the work that has been done so far on learning progressions in science, examine the challenges to developing usable learning progressions, determine if further investments are warranted, and if so, what investments are needed to realize their promised benefits. The report examines the quality and utility of the work done to date and identifies gaps in the fields that would have to be addressed in order to move the work forward. This report has been informed by discussions and addresses (1) the nature and quality of existing work on learning progressions in science, (2) the essential elements of learning progressions, (3) the outstanding issues, challenges and debates about learning progressions in science, and (4) the research and development that must be done to realize their potential as tools for improving teaching and learning. The recommendations are based on the authors' review of transcripts of the discussions at the panel meetings; review of research reports, papers, and funding awards on learning progressions; and extended conversations with many of the participants in the meetings. Three appendixes are included: (1) CCII (Center on Continuous Instructional Improvement) Science Panel Meeting Participants; (2) Table of Learning Progressions in Science Discussed, Mentioned, and Identified by Panelists; and (3) Examples of Learning Progressions. (Contains 6 footnotes.)