This paper applies the causal mediation framework proposed by Kosuke Imai and colleagues (Imai, Keele, & Tingley, 2010) to educational research by examining the causal mediating role of early literacy activities in parental education influences on reading performance. The paper argues that the study of causal mediation is particularly relevant in educational settings because learning outcomes result from complex interactions involving multiple actors. The analyses use retrospective longitudinal data from the Progress in International Reading Literacy Study (PIRLS) 2011. The value of international assessment data for producing evidence of causation is discussed. The paper aims to contribute to the study of causation with observational data from educational studies.