Final answer:
An adolescent at the 90th percentile for BMI on the CDC growth chart is classified as at risk for overweight, not yet reaching the threshold for obesity, which is above the 95th percentile.
Step-by-step explanation:
An adolescent with a body mass index (BMI) plotted at the 90th percentile on the Centers for Disease Control and Prevention growth chart would be considered at risk for overweight. Obesity is generally diagnosed when an adolescent's BMI is greater than the 95th percentile compared to reference values for children of the same age. Therefore, being in the 90th percentile suggests that the adolescent's BMI is higher than that of 89 percent of their peers, putting them at risk for being overweight.