OBJECTIVE: To investigate the impact of increasing levels of inattention, hyperactivity/impulsivity, and oppositional/defiant behaviors at age 7 years on academic achievement at age 16 years. METHOD: In a population-based sample of 7-year-old children in England, information was obtained about inattention, hyperactivity/impulsivity, and oppositional/defiant behaviors (using parent and teacher ratings) and the presence of attention-deficit/hyperactivity disorder (ADHD) and disruptive behavior disorders (DBDs). After adjusting for confounder variables, their associations with academic achievement in national General Certificate of Secondary Education (GCSE) examinations (using scores and minimum expected school-leaving qualification level [5 "good" GCSEs]) at age 16 years were investigated (N = 11,640). RESULTS: In adjusted analyses, there was a linear association between each 1-point increase in inattention symptoms and worse outcomes (2- to 3-point reduction in GCSE scores and 6% to 7% (10%-12% with teacher ratings) increased likelihood of not achieving 5 good GCSEs). ADHD was associated with a 27- to 32-point reduction in GCSE scores and, in boys, a more than 2-fold increased likelihood of not achieving 5 good GCSEs. In boys, oppositional/defiant behaviors were also independently associated with worse outcomes, and DBDs were associated with a 19-point reduction in GCSE scores and a 1.83-increased likelihood of not achieving 5 good GCSEs. CONCLUSION: Across the full range of scores at a population level, each 1-point increase in inattention at age 7 years is associated with worse academic outcomes at age 16. The findings highlight long-term academic risk associated with ADHD, particularly inattentive symptoms. After adjusting for inattention and ADHD respectively, oppositional/defiant behaviors and DBDs are also independently associated with worse academic outcomes.