In order to predict the earnings of single mothers under the Temporary Assistance to Needy Families (TANF) program and the success of welfare reform in reducing poverty, a study was conducted of single mothers' work behavior, welfare receipt, and other sources of income. Data were generated from the U.S. Census Bureau's Survey of Income and Program Participation (SIPP) from 1984, 1986, 1987, 1988, 1990, and 1991. Results strongly suggest that welfare recipients who are required to work as a result of welfare reform will likely do worse in the labor market than single mothers who are already working. They have less education and work experience, which are likely to lead to lower earnings, and higher child care costs per employment hour, since they have more and younger children. Their earnings will likely be low--well below the poverty level--and their child care costs will consume much of their earnings. They will therefore need considerable ongoing financial assistance in order to enable them to hold jobs and to maintain their already-low standard of living. Reforms such as a higher minimum wage, temporary disability insurance programs, allowing welfare recipients to package earnings along with benefits, and providing child care subsidies and health insurance to low-income mothers would help low-income mothers to become self-supporting. (KC)