Objective: Examine academic achievement of students with attention-deficit hyperactivity disorder (ADHD) during the early high school period and identify potentially modifiable risk factors for low achievement. Method: Data were collected through surveys (adolescent, parent, and teacher) and direct assessment of Australian adolescents (12-15 yr; n = 130) with ADHD in early high school (i.e., US middle and high school grades). Academic achievement outcomes were measured by linking to individual performance on the National Assessment Program-Literacy and Numeracy (NAPLAN) tests, direct assessment of reading and math, and teacher report of academic competence. Linear regression models examined associations between adolescent, parent/family, and school factors and NAPLAN domain scores. Results: Students with ADHD had lower NAPLAN scores on all domains and fewer met minimum academic standards in comparison with state benchmarks. The poorest results were for persuasive writing. Poor achievement was associated with lower intelligence quotient across all academic domains. Adolescent inattention, bullying, poor family management, male sex, and attending a low socioeconomic status school were associated with lower achievement on specific domains. Conclusion: Students with ADHD are at increased academic risk during the middle school and early high school period. In addition to academic support, interventions targeting modifiable factors including inattention, bullying, and poor family management may improve academic achievement across this critical period.