The overall purpose of the study was to investigate how two different grading systems, the norm-referenced and the criterion-referenced garaging systems influence the educational achievement for children and youths placed in out-of-home care (individuals who at some time point between ages 0 to 21 years have been placed in out-of-home care). Background variables and variables reflecting the characteristics of the placement was taken into account in the analyses. Another purpose was to investigate the trends in educational achievement for placed and not placed individuals within the different grading systems. Academic results were measured by Grade Point Average in 9th and 12th Grade (GPA 9 for 15–16 year olds and GPA 12 for 18–19 year-olds) and educational attainment in terms of graduation from upper secondary school. In all, 1,936,913 individuals born between 1973 and 1990 participated in the study. The analyses of the placed children and youths´ achievement (N = 67,157) showed a negative effect of the criterion-referenced grading system when controlling for background characteristics and characteristics of the placement. In sum, experience of a criterion-referenced (non-compensatory) grading system, being older when placed and experiencing more placements, is associated with a negative achievement trend for the children and youth placed in out-of-home care. The results show effect sizes of Cohen's d of 1.06 between individuals not placed M = 50.96 (49.92–50.01) and placed M = 22.43 (22.26–22.61) in out-of-home care, for GPA in 9th Grade, with benefits for not placed individuals. The corresponding effect size for GPA in 12th Grade was Cohen's d 0.61 not placed M = 50.10 (49.76–49.86) and placed M = 32.87 (32.55–33.19).