The purpose of this study was to examine how participation in an inquiry-based science program impacts kindergarten students' science learning and motivation. The study was implemented as part of a larger, federally funded research project, the Scientific Literacy Project or SLP (Mantzicopoulos, Patrick, & Samarapungavan, 2005). The study provides descriptive data on the science learning and motivation of public kindergarten students who participated in a year-long implementation of a series of inquiry-based science units as part of SLP. The students who learned science through guided-inquiry (the INQ group) completed six inquiry-based science units over the course of the school year. Data were also collected from a group of kindergarten students (the COMP group) who received regular science instruction on a similar set of topics to the INQ group but did not use the inquiry-based SLP approach to science. Data from this latter group helped us better understand the extent to which the patterns of conceptual development observed in the children who learned science through inquiry could be attributed to the features of the research-based SLP curriculum rather than other factors like maturation or the mere exposure to any science instruction. There were 186 students who participated in the study (118 INQ and 68 COMP students). A variety of measures, including researcher-developed measures of learning and motivation as well as standardized measures of achievement, were administered to both groups. Statistical analyses of pre and posttest performance showed that INQ students made significant gains across all measures of science learning from the beginning to the end of the school year. They developed an enhanced functional understanding of scientific inquiry. (Contains 5 figures and 10 tables.)