Importance  To better support children with the experience of parental death, it is crucial to understand whether parental death increases the risk of adverse school outcomes.

Objectives  To examine whether parental death is associated with poorer school outcomes independent of factors unique to the family, and whether children of certain ages are particularly vulnerable to parental death.

Design, Setting, and Participants  This population-based sibling cohort study used Swedish national register-based longitudinal data with linkage between family members. Register data were collected from January 1, 1990, to December 31, 2016. Data analyses were performed on July 14, 2021. The participants were all children born between 1991 and 2000 who lived in Sweden before turning age 17 years (N = 908 064).

Exposure  Parental death before finishing compulsory school.

Main Outcomes and Measures  Mean school grades (year-specific z scores) and ineligibility for upper secondary education on finishing compulsory school at age 15 to 16 years. Population-based cohort analyses were conducted to examine the association between parental death and school outcomes using conventional linear and Poisson regression models, after adjustment for demographic and parental socioeconomic and health indicators measured before childbirth. Second, using fixed-effect linear and Poisson regression models, children who experienced parental death before finishing compulsory school were compared with their siblings who experienced the death after. Third, the study explored the age-specific associations between parental death and school outcomes.

Results  In the conventional population-based analyses, bereaved children (N = 22 634; 11 553 boys [51.0%]; 11 081 girls [49.0%]; mean [SD] age, 21.0 [2.8] years) had lower mean school grade z scores (adjusted β coefficient, −0.19; 95% CI, −0.21 to −0.18; P < .001) and a higher risk of ineligibility for upper secondary education than the nonbereaved children (adjusted risk ratio, 1.36; 95% CI, 1.32-1.41; P < .001). Within-sibling comparisons using fixed-effects models showed that experiencing parental death before finishing compulsory school was associated with lower mean school grade z scores (−0.06; 95% CI, −0.10 to −0.01; P = .02) but not with ineligibility for upper secondary education (adjusted risk ratio, 1.07; 95% CI, 0.93-1.23; P = .34). Independent of birth order, losing a parent at a younger age was associated with lower grades within a family.

Conclusions and Relevance  In this cohort study, childhood parental death was associated with lower school grades after adjustment for familial confounders shared between siblings. Children who lost a parent may benefit from additional educational support that could reduce the risk of adverse socioeconomic trajectories later in life.