An individual’s, and indeed the nation’s, social and economic futures are highly dependent on early childhood development (ECD) outcomes, with poor ECD inhibiting future opportunities. Ecological ECD literature describes family, community and institutions as being key factors in children’s wellbeing, with suggestions that community factors may ameliorate impacts of poor ECD. It is therefore important to develop a greater understanding of those modifiable factors that positively, and negatively, affect ECD outcomes so as ECD policy and practice can be designed and implemented effectively. One approach to this analysis is through the identification and analysis of influencing factors identified within off-diagonal communities—that is those communities where children have either developed well in consideration of their high-levels of socio-economic disadvantage, or developed poorly in consideration of their low levels of socio-economic disadvantage. In this paper we describe a new method for the identification of off-diagonal communities. The method provides a clear and transparent approach to community selection, including a range of methods to further interrogate the community selection ensuring a rigorous and considered selection process. This new method, based on population Census and Australian Early Development Census data, provides the first step in identifying community factors likely to facilitate childhood wellbeing. These findings could inform policy making to reduce inequities by assisting in policy and service delivery design targeted to community needs.