The United States is experiencing a shortage of STEM workers, with many students leaving the pipeline before attaining a career in STEM. STEM education researchers have identified factors at the high school and college level that contribute to attrition, but earlier life events remain underexplored. In this work-in-progress paper, we examine childhood experiences through the lens of qualitative analyses and discuss our ongoing development of an overall understanding of the relevant life and academic "themes" that shape students' lives before entering secondary school. We are currently testing our seven-theme model on the OpenStax Kinetic large-scale research infrastructure using quantitative surveys of participants' biographical data. Our findings from this study will inform future refinement of the survey and its themes, with a particular emphasis on understanding the influence of contextual demographic and psychosocial factors. Over the longer-term, we hope to support research that identifies critical early STEM experiences and offers insight into where certain students might benefit the most from additional STEM support or experiences. [This paper was published in: "Proceedings of the Tenth ACM Conference on Learning @ Scale (L@S '23), July 20-22, Copenhagen, Denmark," ACM, 2023, pp. 368-72.]