This study examined the extent to which continuities and discontinuities in cognitive performance between ages 5 and 10 predicted adult income, educational success, household worklessness, criminality, teen parenthood, smoking, and depression. Assessed were the degree of this change during middle childhood, the influence of socioeconomic status (SES) on this change, and the extent to which this change influenced adult outcomes. The analyses were conducted on 11,200 individuals from the UK Birth Cohort Study who were born in 1970 and who were resurveyed at ages 5, 10, 16, 26, and 30. Substantial discontinuities emerged during middle childhood, with strong SES influences. Changes in middle childhood strongly affected adult outcomes, often outweighing the effects of cognitive development before age 5.