Research Findings: This paper reports on children's use of science materials in preschool classrooms during their free choice time. Baseline observations showed that children and teachers rarely spend time in the designated science area. An intervention was designed to "market" the science center by introducing children to 1 science tool, the balance scale. Baseline measures showed that children did not know the scale's name or function. The intervention was expected to increase children's use of the science area and their knowledge about the scale. Children's voluntary presence and exploration in the science area increased after the balance scale intervention compared to in comparison classrooms. Furthermore, children who participated in this intervention demonstrated improved knowledge about the scale's function, whereas students in the comparison group did not. Practice or Policy: Adults can increase children's autonomous exploration of science tools and materials, and their knowledge about them, by offering particular kinds of large-group learning experiences. (Contains 2 footnotes, 1 table, and 2 figures.)