In this study, we developed machine learning algorithms to automatically score students' written arguments and then applied the cognitive diagnostic modeling (CDM) approach to examine students' cognitive patterns of scientific argumentation. We abstracted three types of skills (i.e., attributes) critical for successful argumentation practice: making claims, using evidence, and providing warrants. We developed 19 constructed response items, with each item requiring multiple cognitive skills. We collected responses from 932 students in Grades 5 to 8 and developed machine learning algorithmic models to automatically score their responses. We then applied CDM to analyze their cognitive patterns.