There is currently a considerable body of research suggesting that parental involvement is linked to young people's attainment at school. It is also generally agreed that a number of factors such as parental background, attention, warmth and parenting style are associated with children's later life outcomes. However, although widely assumed on the basis of these associations, the nature of this causal link has not yet been established. This paper summarises what would be needed to demonstrate that enhanced parental involvement produced better attainment and other outcomes, based on establishing an association, the correct sequence of events, sensitivity to intervention and an explanatory mechanism. It then reports on the findings of a systematic review of available and relevant studies, based on this approach. The search for evidence on the impact of attitudes, expectations and behaviour on attainment yielded 1,008 distinct reports. Of these, 77 were directly about the impact of parental involvement. These confirm that parental involvement and attainment are linked, and in the correct sequence for a causal model. There are several plausible mechanisms to explain why parental involvement might have an impact. And most crucially and unlike all other areas linking attitudes and behaviour to attainment, there is promising evidence that intervening to improve parental involvement could be effective.