The term "developmental delay" includes deficits such as Down syndrome, autism and other genetic or acquired disturbances that disrupt intellectual or social development. Signs of developmental delay are usually first apparent well before adolescence, because your child will not have met developmental milestones on time throughout his childhood. You may be uncertain if your teen has fine motor, language, social or thinking impairments, however, if you are in a new step-parent to a teen or if the delay is more subtle. If in doubt, voice your concerns to your teen's physician, who can arrange for a professional evaluation.
Monitor your teen's need for supervision. Most developmentally delayed teens' development becomes arrested after a certain level, in many cases around the sixth grade, so the amount of supervision a delayed teen needs tends to be more intensive than for a teen who is not impaired, according to the Child Study Center at NYU Langone Medical Center.
Look for delayed-onset adolescence, compared to his peers. Many teens with developmental delays begin their adolescence after age 13, compared to the usual onset of age 9 to 13 for those without developmental delays, according to the website Psychology Today. Because he may enter adolescence at a much later date, behavioral changes in your developmentally delayed teen may be more dramatic and his behaviors more erratic than other teens.
Watch for difficulty interpreting social cues. For example, if your teen has autism he may have flat facial expressions, a monotone or rehearsed-sounding voice, may talk only about himself during conversations, may respond inappropriately, may have problems understanding others' emotions and he may be preoccupied with one or two subjects.
Look for repetitive behaviors that don't serve a purpose, such as repetitive hand gestures, arm flapping or a tendency to walk on his tip toes when he's stressed. Unusual responses like this could be a sign of a developmental delay, such as autism, according to CRC Health Group website. Autistic teens may also show unusual responses to lights, sounds and textures.