Child care is a fact of life in America today. More than two-thirds of all children under the age of five are cared for on a regular basis by someone other than a parent. These children may attend day-care centers or nursery schools, go to the home of a provider who tends to a number of children, or be cared for by a relative, neighbor, baby-sitter, or nanny.

Since welfare reform in 1996, more mothers have had to find child care as they begin to enter the workforce and meet the new work requirements and time limits. From 1997 to 1999, for example, the share of current welfare recipients working for pay rose from 22 percent to 32 percent.

Expanded child-care needs in the wake of welfare reform have also led to a large increase in the day-care money available to states. In fiscal year 1997, $4.2 billion in state and federal funds went toward this purpose, a 35 percent rise from the previous fiscal year.

Both of these factors -- more mothers needing child care and more funds in public coffers to pay for it -- have brought renewed attention to the issue of child-care quality, especially for low-income children or those in current or former welfare-dependent households. This attention reflects, in part, a growing recognition that child-care quality is important both to mothers' employment and children's development.

Fortunately, research is providing valuable insights into the link between child care and child outcomes. In the last several years, three major reviews of the research literature by distinguished bodies of scholars have addressed this topic. A good example is From Neurons to Neighborhoods: The Science of Early Childhood Development, released by the National Research Council and the Institute of Medicine in 2000. In the words of the report: "Higher quality care is associated with outcomes that all parents want to see in their children, ranging from cooperation with adults to the ability to initiate and sustain positive exchanges with peers, to early competence in reading and math."

What are the ingredients of high-quality child care? Safe, clean surroundings and appropriate space and equipment are certainly important, but they aren't enough. At the heart of high-quality child care is the nature of interactions between children and caregivers. Research shows that children develop best if relationships with their caregivers are warm, supportive, responsive, and cognitively stimulating. Stability of care is also important, as it is hard to form sustained relationships if caregivers come and go.

How does child care today measure up? While there are no nationally representative studies of child-care quality, generalizations can be made based on multistate research projects that looked at the quality of care. For example, results from a 2000 study by the National Institute of Child Health and Human Development's Early Child Care Research Network suggest that the quality of 61 percent of settings for young children would be rated as either poor (8 percent) or fair (53 percent), with care for infants and toddlers getting the lowest ratings. Such findings provide sufficient cause for concern about the level of care available in the United States, especially for infants and toddlers.

The situation at the other end of the childhood age span -- teens -- is another cause for concern. Recent experimental studies of welfare-to-work programs have found evidence that teens whose mothers participated in these programs were more likely to have behavioral and school problems than children of welfare mothers not enrolled. Such findings suggest that care and supervision are issues for children of all ages.

Overall, the research linking child care and child outcomes bears some caveats. We don't know at this point if the children who do better in high-quality settings are doing so solely because of their child-care experiences or because of a mix of reasons. When mothers go to work, they bring income into their households, they may experience a boost in self-esteem, and they may learn valuable skills that they transfer to their parenting and household management. Such factors may benefit children even if they are in child-care arrangements that are merely adequate. In addition, parents who are more economically advantaged, more educated, and under less stress are more likely to have the resources and energy to search for better-quality care.

The federal government is funding a new wave of experimental studies to sort out how child care affects children's outcomes. Meanwhile, the existing research clearly suggests that child-care quality matters -- and that making high-quality child care available, accessible, and affordable is a worthy public investment.