This study investigated the relation between birth characteristics and numeracy attainment at age 8 years. Using a multilevel approach, the authors analyzed all non-Aboriginal singletons born in Western Australia who attended government schools and participated in a Western Australia-wide numeracy test in grade 3 between 1999 and 2005. Appropriateness of intrauterine growth was expressed as the proportion of optimal growth parameters for gestational duration, infant sex, and maternal height and parity, which was derived from a total population of births without risk factors for growth restriction. After the authors controlled for sociodemographic factors, term birth and proportion of optimal head circumference at birth were associated with higher numeracy scores. Increasing proportion of optimal birth length and being firstborn were associated with relatively higher numeracy scores among children born to mothers residing in the most educationally deprived area. The relative advantage of being born first was also higher for children born to single mothers. In contrast, higher Apgar scores and greater proportion of optimal birth weight were associated with a lower relative advantage for children born to single mothers. In summary, term birth and increased growth in head circumference and length are key birth characteristics associated with higher numeracy scores, especially among disadvantaged children.