Several decades of research has found that early education and care can have a positive effect on children's cognitive, behavioural and social outcomes, particularly if it is of high quality, and particularly for disadvantaged children. However, less is known about the optimum number of hours, including whether this differs by socio-economic background. This new analysis, conducted by Professor Edward Melhuish at the University of Oxford, is from data in the Study of Early Education and Development (SEED). The research looks in greater detail at the impact of the number of hours that young children have in early years education and care, with breakdowns by socio-economic background. The report also looks at how the quality of a child's home learning environment can impact on the effects of time spent in early years provision. [This report was funded by the Sylvia Adams Charitable Trust.]