Background: Scholars and education reformers alike have re-ignited the importance of teaching science in the elementary grades of the public schools of America by disputing the traditional belief that K-4 learners are too young to learn and function within the nature of science learning and experimentation. The consideration rests on the findings that young learners exposed to inquiry-science skills can develop thinking skills which cultivate analytical, evaluative and problem-solving abilities required for advanced grades. This study examines the impact of a 5-day professional development (PD) for Kindergarten teachers in inquiry-science teaching. Aims: The 5-day PD was designed to provide a comprehensive experience of inquiry-based science concepts and pedagogy. Two follow-up 1-day PDs were conducted for additional support. Sample: It was attended by 42 kindergarten teachers in the Los Angeles Unified School District, CA, USA. Method: All participants attended the 5-day PD and responded to an 11 item pre- and post-PD survey addressing teachers' perceptions of their confidence levels and their concerns and interests in implementing the Full Option Science System (FOSS) inquiry-based science curriculum. Results: The difference of means, paired-samples t tests and correlation measures show that the 5-day PD helped increase teacher confidence in teaching a science curriculum, reduced anxieties over a new teaching pedagogy, diminished doubts on resource-availability, and stimulated an increased desire to learn how to assess students' learning in science. Ten of the eleven queries showed statistical significance at the 0.01 level suggesting a high level of success attained in meeting the inquiry-science teaching and learning goals of this PD. Conclusion: Two follow-up 1-day PDs were conducted at three and six month intervals. The 1-day return PDs showed a marked increase in the level of teacher confidence, peer collaboration, and ease in implementing inquiry-based science pedagogy within a new science curriculum. (Contains 5 tables and 4 footnotes.)