Typically, program evaluation agencies in the legislative branch of state government examine programs that have already been implemented. These evaluations often consider whether a program achieved the legislature's original goals or complied with statutory requirements. Program evaluations frequently determine whether executive branch agencies have made appropriate or cost-effective expenditures while operating a program. For practical and political reasons, legislators may be reluctant to seek evaluations of young programs. Public officials may not want to initiate an evaluation until the implementing agency has had a fair chance to get a program up and running. In addition, legislators often recognize that it takes time for a program to establish a track record. If a program has been in place for only a few months, there may be a limited amount of data that evaluators can use to determine whether the program has met its goals. Legislators who advocated for creation of a program may fear a rush to judgment if an evaluation is undertaken too quickly. Although it is fairly uncommon for legislative program evaluation agencies to estimate programs' future impacts, this chapter suggests that such evaluations may be appropriate in certain circumstances. This chapter discusses the possible use of prospective evaluation by a legislative oversight agency. It illustrates reasons and methods for estimating future impacts of the No Child Left Behind Act. (Contains 1 figure.)