Inattention/hyperactivity is a childhood outcome of low birth weight. However, the mechanisms by which low birth weight leads to inattention/hyperactivity are unclear. This study examined arousal, activation, motor speed, and motor coordination as possible mechanisms, attending to sex differences. 823 children (400 males) from Detroit and surrounding suburbs were assessed with the Child Behavior Checklist and the Teacher Report Form and completed experimental tasks to assess vigilance and activation (Continuous Performance Test signal detection parameters) and motor output speed and control (Grooved Pegboard) at 6 years of age. The relationship between birth weight and inattention/hyperactivity was slightly, but not significantly, stronger for boys than for girls. Arousal, motor speed, and motor coordination significantly partially mediated the relationship between birth weight and inattention/hyperactivity for boys and girls. Moderated mediation was found for the pathway between motor coordination and inattention/hyperactivity such that this relationship was stronger for boys than for girls. Sex differences in the associated features of attention symptoms may reflect partially distinct etiological pathways.