Development of instrumentation into MIT App Inventor will allow me to extract patterns of usage, or "trajectories" including working around problems, that programmers employ while working on their projects. These trajectories will be analyzed to develop user models of reasoning and understanding in App Inventor. A comparison study will explore the cognitive differences between blocks-based programming and an equivalent text-based language with identical available high-level abstractions. This work will conclude with a new model of blocks-based cognition, and likely create many recommendations for language development, both visual and textual, and improvements to App Inventor technology and pedagogy.