Educational cost functions are used to estimate the additional costs associated with certain student and school district characteristics. Scholars and policymakers often assert that the results of cost function analysis can be used to distribute state aid more equitably among school districts. This technique, commonly referred to as "costing out," allows state aid to vary with characteristics over which school officials have no control, with weights equal to coefficient estimates. This article reviews the literature that estimates educational cost functions and attempts to facilitate the comparison between the studies' methodologies and results. (Contains 14 tables and 9 footnotes.)