Program participants have been largely excluded as an evidence source in realist evaluations. We test whether and how lived experience as described through life history interviews with pilot program participants can be used as a valid and unique source of data for elucidating context (C)–mechanism (M)–outcome (O) configurations and informing program theory. We use data about “Opening Opportunities,” a program for indigenous adolescent girls in rural Guatemala, to build a theory of change relating to educational attainment. Life histories yield a rich data set that allows probing of quintessential realist questions; capture subtle, hard-to-measure, and longer term contextual factors and mechanisms; elucidate co-occurring CM and MO dyads; help decipher individual- and structural-level contexts; and provide unique additions and refinements to the program theory. Importantly, this work expands potential evidence sources to inform program theory by including the unique insights from those with lived experience.