Most often, no single characteristic may be used to reveal that children are developmentally delayed or at risk of becoming developmentally delayed. There are common signs for developmental delays and the more quickly adults recognize these signs, the sooner children begin receiving medical and educational evaluations and intervention (Bailey & Wolery, 1992).

When children are not at developmental levels typically found in the majority of children their age, they often are classified as either having a developmental delay or at risk of developing a delay. Additionally, when children do not acquire skills such as performing, speaking, and perceiving new experiences as quickly as do other children the same age, they often are classified as developmentally delayed. A third indicator of a developmental delay is based on physical appearance. That is, if children's height or weight is not appropriate for their age or if their head growth, facial features, body proportions or shapes do not appear to be typical, children typically are considered at risk (Bagnato & Neisworth, 1991 ).

The most frequently noted developmental delays during infancy are motor delays. For example, a child who cannot grasp objects or first rolls over several months later than is typical may have a motor delay. In contrast to infancy, during preschool years the most frequently noted delays are speech and language delays (Thurman & Widerstrom, 1990). There are typical developmental milestones for children from birth to age six years. These milestones may be used to help determine whether children are progressing at expected rates or might be developmentally delayed.

Following a developmental screening, children evaluated as having a delay of six months or more in any area of development are generally referred for a more in-depth evaluation. Children who respond in ways that suggest they have hearing or sight impairments should also be referred for in-depth evaluation. The majority of children from birth through five years old who receive early intervention services have moderate to severe levels of developmental delays (U.S. Department of Education, 1995).

Developmental delays are classified within the areas of cognitive, speech and language, physical, social-emotional development, or health impairments. In some cases, a specific delay may be classified under one category by educators and under a different category by psychologists and medical personnel. Combining all categories, children with developmental delays comprise about 7 percent of all children through age twenty-one years (U.S. Department of Education, 1995).

Children younger than school age are often referred to as developmentally delayed rather than using specific category labels. Many characteristics used to describe children as having specific types of developmental delays are seen in all young children. These characteristics are possible signs of developmental delays only when they continue to exist for an extended length of time or are extremely rare.