"Investigations in Number, Data, and Space"[R], published by Pearson Scott Foresman, is an activity-based K-5 mathematics curriculum designed to help students understand number and operations, geometry, data, measurement, and early algebra. Each instructional unit focuses on a particular content area and lasts from two to five-and-a-half weeks. The curriculum encourages students to develop their own strategies for solving problems and engage in discussion about their reasoning and ideas. Students work in a variety of situations, including as individuals, in pairs, in small groups, and as part of the whole class. The What Works Clearinghouse (WWC) identified two studies of "Investigations in Number, Data, and Space"[R] that both fall within the scope of the Elementary School Mathematics topic area and meet WWC evidence standards. One study meets WWC evidence standards without reservations, and one study meets WWC evidence standards with reservations, and together, they include more than 8,000 students in grades 1-2 and grades 4-5 in 16 districts across 13 states. One of the studies examined math achievement after students experienced the curriculum for two years, while the other examined students after one year of curriculum experience. The WWC considers the extent of evidence for "Investigations in Number, Data, and Space"[R] on the math performance of elementary school students to be medium to large for one outcome domain--mathematics achievement--examined for studies reviewed under the Elementary School Mathematics topic area. Appended are: (1) Research details for Agodini et al. (2010); (2) Research details for Gatti & Giordano, 2010; (3) Outcome measures for mathematics achievement domain; (4) Findings included in the rating for the mathematics achievement domain; and (5) Description of supplemental findings from Year 1 for the mathematics achievement domain. A glossary of terms is included. (Contains 5 tables and 9 endnotes.)