This study provides evidence on the immediate and long-term effects of parental separation and union dissolution on children’s test scores. We use administrative full population data on parents moving out of the joint home and national school-administered low-stakes test. First, a staggered event-study design finds long-term negative effects on test scores with indications of a dynamic effect increasing by time since separation. Results hold when applying recent innovation in difference-in-differences methods. Further, the decline in test scores originates from the middle of the skill distribution. Second, we demonstrate plausible indications of an immediate negative effect of parental separation on children’s test scores using a regression discontinuity design, with the difference in time between test date and parental separation as the running variable.