The impact of California Work Opportunity and Responsibility to Kids (CalWORKS), which was passed to increase California welfare recipients' participation in welfare-to-work (WTW) activities, was examined. The impact study consisted of a nonexperimental program evaluation that used statistical models to estimate causal effects and a simulation designed to identify the effect of California's benefit structure on the state's work activities participation rate. The study revealed nearly continuous improvements in almost all CalWORKS outcomes since approximately 1993. California welfare recipients' participation in WTW activities and their employment and earnings have risen sharply, the welfare caseload has fallen sharply, employment and earnings of those leaving welfare have risen, and poverty has fallen. Interstate comparisons were mixed. Compared with the rest of the nation, California's rates of participation in WTW activities were higher, but its decline in welfare caseload was lower. The start of the improvements coincided with the recovery of California's economy from a deep recession. (Thirty-eight tables/figures are included. The following items are appended: an overview of possible influences on outcomes; descriptions of the study's data sources and analytic methods; results of the policy simulation; and data on caseload decline by California region and county. The bibliography lists 239 references. A separate executive summary that contains 13 tables/figures is included.) (MN)