The purpose of this action research was to understand how reflective, job-embedded early childhood science professional learning and development (PLD) impacted Early Head Start (EHS) teacher learning and their perceptions toward science with toddlers. Limited content knowledge and lack of formal preparation impact teachers' understanding of developmentally appropriate science and their capacity to support children to develop science skills. In Arizona, limited availability of early childhood science coursework and no science-related PLD for toddler teachers showed the need for this project. Four literature themes were reviewed: teacher as researcher, how people learn, reflective PLD, and how young children develop scientific thinking skills. The participants were nine EHS teachers who worked at the same Head Start program in five different classrooms in Arizona. The innovation included early childhood science workshops, collaboration and reflecting meetings (CPRM), and electronic correspondence. These were job-embedded, meaning they related to the teachers' day-to-day work with toddlers. Qualitative data were collected through CPRM transcripts, pre/post-project interviews, and researcher journal entries. Data were analyzed using constant comparative method and grounded theory through open, focused, and selective coding. Results showed that teachers learned about their pedagogy and the capacities of toddlers in their classrooms. Through reflective PLD meetings, teachers developed an understanding of toddlers' abilities to engage with science. Teachers acquired and implemented teacher research skills and utilized the study of documentation to better understand children's interests and abilities. They recognized the role of the teacher to provide open-ended materials and time. Moreover, teachers improved their comfort with science and enhanced their observational skills. The teachers then saw their role in supporting science as more active. The researcher concluded that the project helped address the problem of practice. Future research should consider job-embedded PLD as an important approach to supporting data-driven instructional practices and reflection about children's capabilities and competencies. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]