The associations between (dimensionally scored) measures of attentional difficulties at age 8 and psychosocial outcomes at age 18 were examined in a birth cohort of New Zealand children. Increasing attentional difficulties during middle childhood were associated with increased risks of academic failure or difficulties, juvenile offending, and substance use behaviours in young adulthood. However, those with early attentional difficulties were a high-risk group characterised by social disadvantages, early conduct difficulties, lower IQ, and related characteristics. Statistical adjustments showed: (a) that attentional difficulties were related to later academic success even when due allowance was made for potentially confounding factors; and (b) early attentional difficulties were unrelated to later juvenile offending or substance use behaviours after adjustment for confounding. In all cases there was evidence of consistent dose/response relationships between the extent of early attentional difficulties and later academic outcomes, suggesting that these associations were not confined to those with extreme symptoms.