Although children develop at different rates and, therefore, the notion of interindividual differences exists, a single child can show more rapid change in some developmental areas than in others; thus, intraindividual differences also exist. Regardless of the perspective, there are certain principles of development that apply to all children. These include the following:

  • Development progresses in a step-by-step fashion. It is orderly, sequential, and proceeds from the simple to the complex. Each achieved behavior forms the foundation for more advanced behaviors.
  • Rates of development vary among children as well as among developmental areas in a single child.
  • Development is characterized by increasing specificity of function (differentiation) as well as integration of these specific functions into a larger response pattern. A good example of this principle is the infant startle reflex. When an infant is startled, his entire body tenses and his arms move out to the side. With age, this reflex becomes integrated into more specific behavioral patterns such that a startled preschooler will tense only the shoulder and neck muscles.
  • Neurological development contributes significantly to the acquisition of physical skills in young children. Physical development proceeds in cephalocaudal and proximodistal directions. Cephalocaudal development describes the progression of body control from the head to the lower parts of the body. For example, an infant will achieve head, upper trunk, and arm control before lower trunk and leg control. Proximodistal development describes progress from the central portions of the body (i.e., the spinal cord) to the distal or peripheral parts. In this developmental progression, gross motor skills and competencies precede fine motor skills. This developmental progression continues throughout early childhood, with upper trunk control being achieved first, then arm control, and finally finger control. According to this principle, each change in the child’s development should result in an increasingly refined level of skill development.
  • Development of any structure follows a sequential pattern; however, there appear to be specific times during development in which a developing structure is most sensitive to external conditions. These sensitive periods, or critical periods, are the times during which a specific condition or stimulus is necessary for the normal development of a specific structure. Conversely, these periods also represent times when a structure may be most vulnerable to disruption (Rice & Barone, 2000). The concept of critical periods has created much debate in theoretical circles, particularly with respect to parent–infant bonding (Anisfeld et al., 1983) and language development (Lenneberg, 1967).
  • All development is interrelated. Although it is convenient for the student or early interventionist to discuss development in terms of discrete developmental areas, such as motor skills, development in other areas such as social-emotional or communication functions does not cease, nor is it necessarily separate from other areas. The student or child practitioner must recognize how different areas of development are interrelated to understand how a particular child develops.
  • Development is influenced by heredity and environment. Although there has been much discussion by experts in the field about which is more important, there is no doubt that they both play a role in a child’s development. A child’s genetic inheritance (i.e., heredity) provides the basic foundation for many physical and personality attributes, but the influences of social, cultural, and familial variables (i.e., environment) also contribute to development.