National Center for Education Statistics
Education Finance Statistics Center Finance Graphs (EDFIN) of the National Center for Education Statistics (NCES) 2008-09 map of the United States and vertical ranking by state illustrating average state funding for K-12.
K-12 Per Pupil Funding and National Average Chart comparing Colorado per pupil funding to the National average 1970 - 2011 using NCES data, Gallagher, TABOR, and Amendment 23 passage also noted. Chart provided by Great Education Colorado.
National Center for Education Statistics (NCES): US Average and Colorado Per Pupil Spending - Adjusted for Inflation FY 1996-FY 2011. Adjusted for inflation, Colorado spent $-1,816 less per pupil than the national average in FY2011. The full NCES report: NCES Revenues & Expenditures for Public Elementary & Secondary Education: School Year 2010-11 (Fiscal Year 2011) is available here.