Many studies have linked quality in early childhood education and care [ECEC] to school performance, but the mechanisms of how ECEC process quality affects children in ways that lead to improved school performance is unclear. In this study on 7431 children in Norway, we test the hypothesis that the relation between process quality in ECEC and later school performance is mediated by early social skills. Process quality was measured at age 5 years along two dimensions: 'pedagogical practices' and 'structured activities', and school performance was measured at age 11 years (5th grade) using mandatory national tests in math, reading, and English. The results show that the indirect effect of pedagogical practices on school outcomes through social skills was small but statistically significant. In contrast, there was no statistically significant indirect effect of structured activities on school performance through social skills.