The Annie E. Casey Foundation's 2012 KIDS COUNT[R] Data Book shows both promising progress and discouraging setbacks for the nation's children: While their academic achievement and health improved in most states, their economic well-being continued to decline. This year's Data Book uses an updated index of 16 indicators of child well-being, organized into four categories: Economic Well-Being, Health, Education, and Family and Community. The new methodology reflects the tremendous advances in child development research since the first KIDS COUNT Data Book in 1990. Appended are: (1) Child Well-Being Rankings; and (2) Data for 16 Indicators of Child Well-Being. (Contains 5 figures and 29 endnotes.) [For "KIDS COUNT Data Book, 2011: State Profiles of Child Well-Being. America's Children, America's Challenge: Promoting Opportunity for the Next Generation," see ED522925.]