Over the last two decades, there has been an increasing focus on spatial technologies in teaching and learning, revealing the potential to support new forms of youth sensemaking across varied settings and modalities. Recent scholarship has shown the possibilities of participatory digital mapping technologies, enabling young people to collect data within community settings and create interactive data-rich maps about complex phenomena and processes that build from their local expertise and inquiries. Yet to date, these technologies and related pedagogies remain less researched within K-5 educational contexts. In this article, we examine the most recent iteration from a multi-year design research project that centered 5th grade students' learning about socio-ecological systems by engaging in participatory digital mapping to study their schoolyard soil ecosystems underfoot. We examine the possibilities of centering digital participatory map making as a basis for modeling and argumentation in elementary science. Analyzing whole class discussion video within the 10-week curriculum, we show how children authored their collective maps in numerous ways, making visible their social and ecological knowledge of the schoolyard, as well as their experiences defining, producing and visualizing qualitative and quantitative data. As part of this broader design-based research project, we find that children were able to reason about complex socio-ecological systems across spatial, temporal, and relational dimensions in inventive ways, often considered out of reach for elementary aged students, while also expanding what could count as data and what ways of knowing were valued within the science classroom. Implications for science education, place-based education, and emerging geospatial technologies are discussed.