A Comparable Wage Index (CWI) is an attractive mechanism for measuring geographic variations in the cost of education. A CWI measures uncontrollable variations in educator pay by observing systematic variations in the earnings of comparable workers who are not educators. Together, the 2000 census and the Occupational Employment Statistics survey support the construction of just such an index. The resulting panel of index values measures wage levels in all parts of the United States from 1997 through 2004 and reveals substantial variation in purchasing power both across school districts and across time. Such inequalities undermine the equity and adequacy goals of school finance formulas. If states were successfully directing additional resources to school districts in high-cost environments, then measured inequality within states should fall when differences in purchasing power are taken into account. Instead, cost adjustment widens the spending gap in all but a handful of states.