As part of a larger project aimed at promoting science and literacy for culturally and linguistically diverse elementary students, this study has two objectives: (a) to describe teachers' initial beliefs and practices about inquiry-based science and (b) to examine the impact of the professional development intervention (primarily through instructional units and teacher workshops) on teachers' beliefs and practices related to inquiry-based science. The research involved 53 third- and fourth-grade teachers at six elementary schools in a large urban school district. At the end of the school year, teachers reported enhanced knowledge of science content and stronger beliefs about the importance of science instruction with diverse student groups, although their actual practices did not change significantly. Based on the results of this first year of implementation as part of a 3-year longitudinal design, implications for professional development and further research are discussed.