Massachusetts' 2006 health reform cut the uninsurance rate for children approximately in half in the first two years following implementation. The state now has the lowest rate of uninsurance among children in the nation. More children became enrolled in MassHealth, the state's Medicaid program, and in employer-sponsored insurance. Most of the coverage increases occurred among lower-income children, many of whom were eligible for but not enrolled in MassHealth prior to reform. We derive a major lesson for national health reform: that outreach, enrollment simplifications, and coverage expansions to parents and children can lead to substantial reductions in the number of uninsured children, particularly among children in the lowest-income families.