title: Age, academic performance, and stimulant prescribing for ADHD: a nationwide cohort study.
abstract: BACKGROUND
  We evaluated whether younger age in class is associated with poorer academic performance and an increased risk of being prescribed stimulants for attention-deficit/hyperactivity disorder (ADHD).
  
  
  METHODS
  This was a nationwide population-based cohort study, linking data from national registries of prescribed drugs and standardized scholastic examinations. The study population comprised all children born in 1994-1996 who took standardized tests in Iceland at ages 9 and 12 (n = 11 785). We estimated risks of receiving low test scores (0-10th percentile) and being prescribed stimulants for ADHD. Comparisons were made according to children's relative age in class.
  
  
  RESULTS
  Mean test scores in mathematics and language arts were lowest among the youngest children in the fourth grade, although the gap attenuated in the seventh grade. Compared with the oldest third, those in the youngest third of class had an increased relative risk of receiving a low test score at age 9 for mathematics (1.9; 95% confidence interval [CI] 1.6-2.2) and language arts (1.8; 95% CI 1.6-2.1), whereas at age 12, the relative risk was 1.6 in both subjects. Children in the youngest third of class were 50% more likely (1.5; 95% CI 1.3-1.8) than those in the oldest third to be prescribed stimulants between ages 7 and 14.
  
  
  CONCLUSIONS
  Relative age among classmates affects children's academic performance into puberty, as well as their risk of being prescribed stimulants for ADHD. This should be taken into account when evaluating children's performance and behavior in school to prevent unnecessary stimulant treatment.
authors.affiliation: Institute for Translational Epidemiology, Mount Sinai School of Medicine, New York, NY 10029, USA. helga.zoega@mssm.edu
authors.forename: Helga
authors.initials: H
authors.lastname: Zoëga
authors.forename: Unnur A
authors.initials: UA
authors.lastname: Valdimarsdóttir
authors.forename: Sonia
authors.initials: S
authors.lastname: Hernández-Díaz
mesh_terms: D000124:Achievement; D000367:Age Factors; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D000697:Central Nervous System Stimulants / Q000009:adverse effects / Q000627:therapeutic use*; D002648:Child; D015331:Cohort Studies; D004521:Educational Measurement; D005260:Female; D006801:Humans; D007055:Iceland; D007803:Language Arts; D008297:Male; D008433:Mathematics / Q000193:education; D010818:Practice Patterns, Physicians' / Q000706:statistics & numerical data*; D012042:Registries; D012307:Risk Factors; D012737:Sex Factors
chemical_list: D000697:Central Nervous System Stimulants