Theories—or models—of human development are intended to account for how and why people grow up as they do. A convenient way to distinguish one type of theory from another is to identify the aspects of life on which different types focus. For example, some concentrate on intellectual development, attempting to explain how people's skills of analyzing and memorizing improve with the passing years. Others center attention on physical development, seeking to clarify how the body as a biochemical organism increases in size, complexity, and coordination. Still other theories concentrate on how people's morally good and morally bad behavior evolves. This third group—the ones intended to explain the development of moral thought and action—is the concern of this book.