Cognitive ability and mental health are arguably two of the most important aspects of child functioning, and both have long-term effects on a range of outcomes. Although studies of children in clinic samples have shown substantial comorbidity between cognitive problems - especially language problems - and behaviour problems, research has not shown how cognitive ability and mental health combine in the general child population, and over time. Using longitudinal data from the UK's Millennium Cohort Study (MCS), we will 1) chart the typical and atypical patterns of this developmental association in the general child population from the early years until the end of primary school, 2) relate these to early family risk and later (adolescent) outcomes, and 3) explore the role of school in these trajectories and in reinforcing or compensating the effects of early family risk on these trajectories. The project is funded by the ESRC