Intact marriage positively associates with the mother's education
Married mothers in intact families tend to be the most educated — more than 38 percent have at least a college degree. By comparison, about 21 percent of mothers in married stepfamilies have at least a college degree, and less than 15 percent of single mothers are college educated.
Mother's education attainment by marital status

Sources: U.S. Census Bureau, Current Population Survey; America's Children: Key Indicators of National Wellbeing, 2011.