Structural equation modelling was used to investigate the predictive associations between kindergarten developmental, socio-behavioural, and biotic influences on third grade achievement among a nationally representative sample of low-SES children. The findings validate the understanding that developmental and learning trajectories start early in children's lives and are influenced by multifaceted factors. Findings also elucidated areas where predictive influences were different among low-SES children than they were for the general. Children residing in low-SES homes are at risk for academic and developmental difficulties. Study findings have established that within a low-SES group of children, disparities in early learning and development exist. Understanding the factors that positively and negatively affect learning and development among low-SES children informs intervention strategies that may moderate the gaps that exist in these areas among SES groups as they progress through school. There were several noteworthy findings related to within-SES differences that potentially impact children's academic trajectories.