A new National Science Foundation supported curriculum, Interactions in Physical Science[TM], was evaluated on students' conceptual change in the twelve concept areas of the national physical science content standard (B) for grades 5-8. Eighth grade students (N = 66) were evaluated pre and post on a 31-item multiple-choice test of conceptual understanding developed by the Harvard-Smithsonian Center for Astrophysics. Significant student gains (p less than 0.05, t-test, two-tailed) occurred in all concept areas in the category of properties and changes in properties of matter; for the force concept areas in the category motions and forces; and for the heat transfer and light interactions areas in the category of transfer of energy. Two of the six concept areas in the category of transfer of energy, chemical and nuclear reactions and the sun as a major source of energy, were not addressed in this study. Significant learning gains as item percent correct were typically close to 20%, though effect sizes were small to medium in magnitude (d = 0.3-0.6). Implications of the study for conceptual change curriculum and teaching are discussed.