Theories lend structure and meaning to the scientific study of children. This chapter provides an overview of philosophical and theoretical approaches to child study from medieval to modern times. It also reviews major research strategies used to study child behavior and development.

When compared and contrasted, historical philosophies and contemporary theories raise three basic issues about what children are like and how they develop: (1) Is development continuous or discontinuous? (2) Is there one course of development or many? (3) Is nature or nurture more important in development? Theories also differ in the degree to which they emphasize stability versus the potential for change. Many theories, especially modern ones, take a balanced point of view and recognize the merits of both sides of these issues.

Research methods commonly used to study children include systematic observation, self-reports, psychophysiological methods, the clinical, or case study, method, and ethnography. Investigators of child development generally choose either a correlational or an experimental research design. To study how their participants change over time, they use special developmental research strategies-longitudinal, cross-sectional, longitudinal-sequential, and microgenetic designs. Each method and design has both strengths and limitations.

Conducting research with children also poses special ethical dilemmas. Ethical guidelines for research and special committees determine if the benefits of research outweigh the risks and ensure that children's rights are protected.