The Discovery Research K-12 program (DRK-12) seeks to significantly enhance the learning and teaching of Science, Technology, Engineering and Mathematics (STEM) by preK-12 students and teachers, through research and development of innovative resources, models and tools (RMTs). Projects in the DRK-12 program build on fundamental research in STEM education and prior research and development efforts that provide theoretical and empirical justification for proposed projects. This project will design and develop a new K-12 classroom observation protocol for integrated STEM instruction (STEM-OP). The STEM-OP will be developed for use in K-12 STEM settings. While the importance of integrated STEM education is established, there remains disagreement on models and effective approaches for integrated STEM instruction. This issue is confounded by the lack of observation protocols sensitive to integrated STEM teaching and learning to inform research to the effectiveness of new models and strategies. Existing instruments were not developed for use in integrated STEM learning environments. The STEM-OP will be designed to be used effectively by multiple stakeholders in a variety of contexts. Researchers will benefit from having the STEM-OP available for them to carry out research and continue to improve STEM education in a variety of ways. Existing instruments were not developed for use in integrated STEM learning environments. The STEM-OP and associated training materials will be available for use by other education stakeholders, such as K-12 teachers and district administrators, through a publicly available online platform. In brief, the STEM-OP will inform the instruction of integrated STEM in many contexts with the goal of improving integrated STEM education.The primary product of this project is the new observation protocol called STEM-OP for K-12 classrooms implementing integrated STEM lessons. The project will use over 500 integrated STEM classroom videos to design the STEM-OP. Using exploratory and confirmatory factor analysis, the STEM-OP will be a valid and reliable instrument for use in a variety of educational contexts. The research will explore the different ways that elementary, middle, and high school science teachers enact integrated STEM instruction. This study will shed light on the nature of STEM instruction in each of these grade bands and provide information building towards an understanding of learning progressions for engineering practices across grade bands. Research exploring how the nature of STEM integration changes from day to day over the course of a unit will provide critical information about the different sequencing and trajectories of STEM units. Examining how integrated STEM instruction unfolds over a full unit of instruction will inform the understanding of integrated STEM practices at both micro- and macro- levels of analysis. The STEM-OP and associated training materials will be available for use by other education stakeholders, such as K-12 teachers and district administrators, through a publicly available, which will be distributed via a publicly available, online platform that includes a training manual and classroom video for practice scoring.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.