This research investigated whether delayed school entry was associated with higher achievement in national tests of reading and numeracy in Grades 3, 5, 7, and 9 (<i>n</i> = 2,823). Delayed entry was related to advantages in reading (0.14 <i>SD</i>) and numeracy (0.08 <i>SD</i>) at Grade 3, although little variance was explained (1%–2%). This slight advantage persisted for both domains in Grades 5 and 7, albeit with smaller effects. In Grade 9 there was no association between delayed entry and either reading or numeracy. Exploratory analyses with subsamples in each grade (<i>n</i> = 424–667) revealed no associations between delayed entry and achievement after controlling for inattention and hyperactivity, and negative associations between inattention and achievement in all grades in both domains (−0.33, −0.49 <i>SD</i>).