In this paper, Susannah Loeb shows that none of the available methods for estimating what it would cost to reach high standards for all children is adequate to the task. This is true for several reasons. It is not possible to map backwards from success because no state now meets the standards to which it aspires. In addition, student needs vary tremendously so the "right" amount in one locality could be inadequate or excessive elsewhere, prices of key inputs vary significantly from one state or locality to another, and many districts lack the capacity to use funds effectively. Moreover, as she concludes, reaching our goals will require innovations in curricula and instruction that are unknown today and therefore cannot be costed-out.