For pediatricians and parents, one of the most important tools is decidedly low tech. The growth chart, a simple graph of the trajectory of the normal range of height, weight, and head circumference across age, is a vital tool for detecting problems in development. Even when a child is in the normal range, identifying a change from the 80 th percentile at age 6 to the 20 th percentile at age 8 can indicate a problem.

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