This paper reports findings from a two-year investigation on the impact of a professional development (PD) program on second grade teachers' science teaching practice, particularly of the Next Generation Science Standards Science and Engineering Practices (NGSS SEPs). The aims of this study were three-fold: 1) identify which SEPs teachers enacted during classroom instruction at the start and end of the PD; 2) explore the ways in which the SEPs were enacted; and 3) explore trends in self-efficacy and confidence of teaching the NGSS SEPs at mid and end points of the PD compared to the start of the program. Analysis of classroom observations revealed that, at time 2 (end of PD), teachers tended to incorporate more of the practices into instruction, with the greatest increase experienced by SEP 7 Engaging in Argumentation. Students also played a more active role in enacting each practice. Classroom observations revealed that, at both time 1 and time 2, teachers successfully utilized both general and SEP-specific scaffolds to support student enactment. Moreover, rather than teaching each practice in isolation, teachers integrated practices together to reach their lesson objective. While students were able to successfully enact most of the practices, they tended to struggle with specific aspects of argumentation and explanation. Finally, teachers experienced significant growth in self-efficacy and confidence of teaching the SEPs as well as in actual classroom practice.