We aimed to estimate the prevalence of risk for developmental and behavioural problems for children in their first year of full-time primary education in the Australian Capital Territory (ACT). We conducted an analysis of the 2014-2017 Kindergarten Health Check (KHC), an annual series of complete enumeration surveys of all children in their first year of full-time primary education in the ACT. Risk for developmental and behavioural problems was determined using the Parents' Evaluation of Developmental Status (PEDS) questionnaire. 19 414 children (mean age 5.56 years; 51.4% boys; 2.3% Aboriginal and Torres Strait Islander; 18.4% quintile of greatest relative disadvantage) who participated in the 2014-2017 KHC were included in the study (87%). More than half of ACT children in their first year of primary education had low/no developmental risk identified through the PEDS questionnaire, with 1 in 10 at high risk. Those more likely to have a high risk PEDS score were boys, those from the areas experiencing relative disadvantage, and Aboriginal and Torres Strait Islander children. While we can identify children at risk through screening, the greater challenge remains to identify and address the underlying causes of healthy inequalities, even within highly socioeconomically advantaged communities.