To determine literacy and numeracy outcomes, among children with and without ADHD by gestational age and gender. De-identified linked population data from the Western Australian Monitoring of Drug Dependence Systems, Western Australian Literacy and Numeracy Assessment database, and the Midwives Notification System used information on 6,819 children with ADHD compared with 14,451 non-ADHD children. Twenty-three percent of boys and 28% of girls with ADHD had numeracy scores below the benchmark in School Year 3, compared with 11% of children without ADHD. These differences were also evident in reading, writing, and spelling through primary school. Children with ADHD and reduced gestational age were at a greater risk of not meeting numeracy and reading benchmarks, compared with children born at term. Children with ADHD are disadvantaged from an early age in key areas of learning, and this risk increased with reduction in gestational age at birth.