The relationship between conduct disorder and attention deficit behaviours in middle childhood (6, 8 and 10 years) and juvenile offending and academic achievement were examined in a birth cohort of New Zealand children. The application of structural equation modelling methods suggested that early behavioural tendencies are related to later developmental outcomes by two highly correlated but distinct developmental progressions. In the first such progression, early conduct disorder behaviours acted as a precursor of future offending patterns but these behaviours were unrelated to later school performance when the correlation between conduct disorder and attention deficit was taken into account. In the second developmental progression early attentional/cognitive behaviours were related to future school performance but were unrelated to the development of antisocial behaviours when the correlations between conduct disorder and cognitive/attentional variables were taken into account. The implications of these findings for validating the distinction between conduct disorder and attention deficit behaviours is discussed and the problems of analysing and explaining the high comorbidity between conduct disorder and attention deficit behaviours are considered.