The NSF ECR Building Capacity of STEM Education Research (BCSER) program contributes to the NSF mission 42 U.S. Code Chapter 16 by building the US workforce undertaking STEM education research. The BCSER Individual Investigator Development in STEM Education Research (IID) track supports individual investigators who are experienced STEM education researchers to develop expertise in new areas that will contribute to advancing STEM education knowledge. STEM education research generates the knowledge, theories, and understandings on which viable strategies for improving U.S. STEM education and workforce outcomes are based. This study focuses on mathematical argumentation in the elementary classroom. It involves the development of a scalable tool to analyze and assess the quality of argumentation in elementary mathematics classrooms, combining AI, psychometrics, and argumentation theory. With two focused studies, it aims to improve learning for struggling students and enable large-scale analysis of classroom discourse in elementary mathematics contexts. This BCSER IID project will allow the PI to supplement their current expertise with new research skills to design and implement cutting edge STEM education research using modern methods and tools. The project will assist the PI to develop new expertise in three intersecting areas: psychometrics, argument theory, and technologies using Large Language Models (LLM) and AI. Specifically, the principal investigator will gain new expe