Kids and Developmental Milestones: What’s the Connection?

Everyday Einstein talks with Nicholas Day, author of Baby Meets World, about the surprising truth behind developmental milestones in babies. (Hint: They don’t matter as much as you think!)

Lee Falin, PhD,
May 10, 2013
Episode #053

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Of course, half of all children will always be beneath the median—otherwise it wouldn’t represent the fiftieth percentile. “In other words,” as the pediatrician Laura Sices has written, “After reviewing 50th percentile milestone information, as many as half of parents could conclude that their child is possibly ‘delayed.’” Instead of medians, it would make far more sense, in almost all circumstances, to talk about the tenth to ninetieth percentiles—the vast age range of normal variation.

Even these broad parameters risk being too narrow, though. In a recent study, 45 infants were assessed monthly on their motor skills until they were 18 months old. During this time, their percentile rankings for motor skills rose and fell wildly, for no apparent reason. Sometimes the babies had small flurries of accomplishment; sometimes they fell into a rut. Nearly a third of them ranked below the tenth percentile at least once—the red line for “at risk” development. But every one of them ultimately turned out just fine. None actually warranted the “at risk” label.

Time and again, studies have failed to predict future problems from motor development measures, and once you grasp just how many infants appear at risk, you realize why such studies keep failing: at any random point in time, a perfectly healthy baby is indistinguishable from an infant with developmental problems. By design, developmental screening is guaranteed to return scores of false positives.

Should We Stop Tracking Developmental Milestones?

Given how crucial early intervention can be, doctors and therapists will never stop screening for developmental problems, nor should they. But since it is so tricky to identify delays, they might never get much better at it, either. Medically, we may always have to trade a preschool’s worth of false positives (needless anxiety about developmental problems) for a few accurate diagnoses (actual developmental problems). That’s probably a trade worth making: for children with serious problems, early therapy can be extraordinarily beneficial. But the rhetoric of milestones doesn’t imply that doctors and therapists have to make this sort of trade. It implies a precision that’s the very opposite of the reality.

See also: Coping with a Special Needs Diagnosis


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