There is surprisingly limited information on how much individuals know about the policy rules that could affect them, either in general or in evaluations of new programs. In this article we examine the level of knowledge that participants in a Wisconsin child support and welfare demonstration had about child support policy rules. We find very low levels of knowledge. Our results suggest that people tend to learn policy rules by experience; we find less consistent support for knowledge being primarily imparted through interactions with caseworkers. Implications of the lack of participants? knowledge for policy evaluations are discussed.