There have been a lot of theories surrounding babies’ early language development and why some children seem much quicker to pick up words than others. Much has crystallized into this prevailing advice: The more you talk to your baby, the more words she hears, and the more words she will eventually know. In other words, lots of language input will equal lots of language output.

But this simple equation doesn’t tell the whole story, the authors of “NurtureShock” say. After all, two children raised in similarly verbal households can pick up words at very different speeds. So what gives?

New research suggests that parents miss the boat when they constantly babble at their children. Equally crucial is listening to what even a very young baby is saying or doing, and then responding. A New York University laboratory study of similarly well-off families focused on how well mothers responded to their infants’ vocalizations. Then the infants were then tracked according to what new words they acquired over time. Some babies seemed to acquire words a lot faster than others. But why?

The variable that best explained these gaps was how often a mom rapidly responded to her child’s vocalizations and explorations. The toddlers of high-responders were a whopping six months ahead of the toddlers of low-responders. … All of the infants heard lots of language. How often a mother initiated a conversation with her child was not predictive of language outcomes—what mattered was, if the infant initiated, whether the mom responded.

Dr. Catherine Tamis-LeMonda, one of the lead researchers, attributes this two a couple of factors: Babies learn that vocalizing prompts their parents to respond, which spurs them to do it more. Also, parents who are quicker to label objects (as a baby is grabbing the object, for instance) better cement that association for their child.

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Michael Goldstein of Cornell University observed moms and babies interact in another laboratory experiment. This time, the mom was directed to touch, pat, or show some sort of physical affection immediately after her baby vocalized. When doing so, the baby vocalized an average of 55 times, compared to 25 when the mother was not instructed to respond in such a way.

It all seems quite simple, then: Let your baby take the lead, but respond quickly. Researchers do offer cautionary notes, though. Overstimulation isn’t the goal — babies do need substantial time when they can play by themselves. Second, take your cues not from what you think your baby is saying, but what he or she is actually observing:

The baby, holding a spoon, might say “buh, buh,” and the zealous parent thinks, “He just said ‘bottle,’ he wants his bottle,” and echoes to the child, “Bottle? You want your bottle?” … Inadvertently, the parent just crisscrossed the baby, teaching him that a spoon is called “bottle.” … Pretending the infant is saying words, when he can’t yet, can really cause problems.

The authors cover some other techniques parents can use to bolster language development. They include the following:

  • “Motionese.” Babies under 15 months benefit when parents shake or move an object as they label it.
  • Multiple speakers. Babies may pick up a word faster if they hear it from a variety of people, rather than the same one over and over.
  • Language frames. Babies tend to hear the last word in a sentence most clearly, so they are primed to learn those first. Saying something like, “Throw me the ball” or “Look at the sun” will teach “ball” and “sun” far faster than “throw” or “look.”

Parents’ ultimate takeaway, according to the authors, should be this: It’s possible to jump-start a child’s language development, but once kids are school-aged, differences tend to shrink considerably. Late talkers commonly catch up to their peers and show no ill effects from ever having been “behind,” especially if they have a large receptive vocabulary – that is, words they can understand, even though they can’t repeat them.

It’s important to characterize early language precocity for what it is: a head start, but far from a guarantee. “It’s not like the infancy period is the only critical period,” said Tamis-LeMonda. “New skills are emerging in every period, and vocabulary development has to continually expand.”

Will you try some of these techniques to help your infant’s language development? Do you have an early or late talker?