Conduct problems and poor language development have been previously associated, however the direction of this association in early childhood remains unclear.

This study examined the longitudinal associations between conduct problems and expressive language ability from three to five years of age. Auto-regressive, concurrent, and cross-lagged paths were investigated while controlling for the contribution of parenting styles, maternal depression, children's cognitive ability, hyperactivity/inattention, and sex.

Children enrolled in the Millennium Cohort Study (MCS) (N = 17, 184), a population-based sample from the United Kingdom, were assessed at three and five years of age. Parent reports of conduct problems and standardized assessments of expressive language were analyzed using a cross-lagged modeling approach.

Conduct problems at three years was associated with poorer expressive language at five years and poorer expressive language at three years was associated with increased conduct problems by five years.

Overall, the results support reciprocal paths between conduct problems and poorer expressive language ability from three to five years of age. Interventions targeting conduct problems, language acquisition, and parenting in the first five years of life may yield the best results in the prevention of both conduct problems and poorer expressive language.