of the nature of early human development. They are summarized here and reemerge repeatedly throughout the report.

Defining the boundaries of science in early childhood development is not an easy task. However, this task can be facilitated for policy makers, practitioners, and parents by differentiating among established knowledge, reasonable hypotheses, and unwarranted assertions (Shonkoff, 2000). Established knowledge is determined by strict rules of evidence and rigorous peer review. It evolves continually over time. Reasonable hypotheses are educated guesses that are derived from, but extend beyond the boundaries of, established knowledge. Although they may be confirmed or disproved by subsequent investigation, they make up a large proportion of the knowledge base that guides responsible policy, service delivery, and parenting practices at any given point in time. Unwarranted assertions distort or misrepresent current knowledge, undermine its credibility, and have the greatest potential to be harmful when they are advanced by those who are viewed as reputable scientists. They are often made to advance commercial goals or an ideological agenda. Ultimately, informed early childhood policy making, effective service delivery, and successful parenting are all dependent on mastery of the existing knowledge base, sound judgment based on reasonable hypotheses, the avoidance of irresponsible practices, and continuous reassessment over time.

Understanding of child development is based on multiple sources of knowledge that include theoretical models, empirical research, program evaluation, and professional experience. The role of theory is to provide a framework for organizing what is known and for guiding further investigation. The role of empirical research and program evaluation is to ask important questions (e.g., How do children learn number concepts?) and to test specific hypotheses (e.g., High-quality child care results in language gains for toddlers from high-risk homes), using a variety of quantitative and qualitative methods. The role of professional experience is to tap the wisdom and judgment of people who work with children in a variety of service settings. Taken together, these diverse sources of knowledge advance understanding of the process of child development and enhance the capacity to promote competence, prevent disorders, and correct maladaptive patterns.

A set of core concepts frames our understanding of the nature of human development during the earliest years of life and lays a foundation for addressing the following questions:

• Is early development highly programmed, so that certain events must

Front Matter (R1-R20)

Executive Summary (1-16)

I. Setting the Stage (17-38)

Rethinking Nature and Nurture (39-56)

The Challenge of Studying Culture (57-69)

Making Causal Connections (70-88)

II. The Nature and Tasks of Early Development (89-92)

Acquiring Self-Regulation (93-123)

Communicating and Learning (124-162)

Making Friends and Getting Along with Peers (163-181)

The Developing Brain (182-218)

III. The Context for Early Development (219-224)

Nurturing Relationships (225-266)

Family Resources (267-296)

Growing Up in Child Care (297-327)

Neighborhood and Community (328-336)

Promoting Healthy Development Through Intervention (337-380)

IV. Knowledge into Action (381-416)

References (417-534)

Appendix A: Related Reports from the National Academies (535-544)

Appendix B: Defining and Estimating Causal Effects (545-548)

Appendix C: Technologies for Studying the Developing Human Brain (549-552)

Appendix D: Biographical Sketches (553-560)

Index (561-588)