Another factor to consider in relation to development is the concept of individual differences. Children develop at different rates. This, in turn, creates variations among individuals (i.e., individual differences). Again, these differences can be either qualitative or quantitative. For children in any preschool classroom setting, the differences in temperament, personality, intelligence, achievement, and physical factors such as height and weight, are noteworthy and reflect a wide range of normal variation. Some children grow rapidly and others grow more slowly. There also are racial and gender developmental variations. During the fetal stage, for example, females mature faster than males do. Further, at birth, the skeletal development of females is about 4 weeks ahead of that of males, and African American children show more rapid skeletal maturation than white children do (Puckett & Black, 2004; Russell et al., 2001; Tanner, 1990).

It is important to understand that the concept of individual differences is the basis upon which one child is compared to another. Also, the existence of these differences constitutes the fundamental premise underlying the development of standardized educational and psychological tests. An understanding of individual differences provides the foundation for recognizing normal variations as well as extreme differences among children and, thus, for identifying those who may have special needs. In general, understanding of the various developmental levels is enhanced by familiarity with the concept of individual differences. As illustrated in the case vignette, Denise has observed some distinct developmental differences between Nathaniel and her other two children. She is worried that these differences could represent developmental delays or deficits.