The ESSP has a research program focused on the development of Learning Progressions in two of our key content foci - Astronomy and Plate Tectonics. These two content foci were chosen because they are the two major organizing conceptual areas in Earth and Space Science instruction, the focus of the ESSP. Learning Progressions are “empirically grounded and testable hypotheses about how students’ understanding of, and ability to use, core scientific concepts and explanations and related scientific practices grow and become more sophisticated over time, with appropriate instruction.” (National Research Council, 2007). In addition to the focus on Astronomy and Plate Tectonics, we are also looking at cross cutting themes around reasoning across deep time and across large scale.