At the request of a Senate subcommittee, this report describes the value of conducting impact evaluations, describes their current use in evaluating selected early childhood education and care programs, and discusses the value of other types of early childhood education and care studies currently promoted and sponsored by the Departments of Health and Human Services (HHS) and Education. Current government-sponsored studies were reviewed for 11 programs that fund early childhood education and care and that serve at least 25,000 children under age 5, including Project Head Start, Even Start, Migrant Education, and State, Preschool, and Infant and Toddler Grants for special education. The report notes that impact evaluations are considered by many to be the best method for determining the extent to which the program, rather than other factors, causes participant outcomes. The design of impact evaluation studies is discussed, with focus on methodological rigor, expense and time required, and ethical issues involved. Findings noted indicate that the two federal programs focused most on early childhood education, Head Start and Even Start, are currently being studied using impact evaluations with experimental designs. One HHS study of Head Start is a 6-year national impact study that will follow children through first grade. Evaluation of the Early Head Start program will collect information about 17 local programs and follow children to their third birthday. The 6-year Even Start evaluation will examine the effectiveness of 18 local programs. The report notes that although Congress mandated study of Even Start's effectiveness, it did not require that an impact evaluation be used. For the other nine programs, impact evaluations are not currently being used to study the effectiveness of the early childhood education and care services they support. The report concludes by noting that HHS and Education promote and sponsor many types of research and evaluation studies, thereby providing agencies with answers to a broad range of questions about program operation. (KB)