Having regular conversations is the most significant thing you can do for your children’s development. This is the message of Dr. Dana Suskind’s important and clear-eyed new book, Thirty Million Words: Building a Child’s Brain.

“No matter the language, the culture, the nuances of vocabulary, or the socioeconomic status, language is the element that helps develop the brain to its optimum potential,” writes Suskind, who is the founder and director of the Thirty Million Words Initiative at the University of Chicago.

Since I have also written a book about the importance of language for children’s brains, it’s not surprising that I would champion this one. But this is a particularly opportune moment to be talking about the power of talk.

In 1995, a landmark study by researchers Betty Hart and Todd Risley uncovered the fact that, in the first three years of life, some children heard thirty million more words than others.  When they entered school at the age of four, the children with more language exposure had an advantage that translated by third grade into bigger vocabularies, better reading skills, and higher test scores.

That sounds important, but Hart and Risley’s results were virtually ignored for a decade or so. For one thing, the study was interpreted as blaming working-class parents, since many (but not all) of the children hearing fewer words came from lower income families.  And some researchers took issue with the perceived emphasis on quantity of language over quality. Finally, many researchers didn’t think the thirty-million-word gap had much to do with how language was actually learned.

Now we know that early language exposure significantly affects the way language networks are built in the brain. Psychologist Anne Fernald of Stanford University, for example, has shown that “a child’s mental processing speed . . . is shaped through rich engagement with language.”

Why does speed matter? It allows babies and toddlers who can interpret familiar words more quickly to pay closer attention to the next word in the sentence. In other words those kids get more out of each verbal experience, boosting vocabulary, and strengthening working memory, reasoning, and conceptual abilities. Building those cognitive skills makes children even better prepared for the next sentence, and the next, and the next. When it comes to language, those rich in skills and experience get richer and the poor are at a distinct disadvantage.

We also know now that quality of conversation matters as much as quantity. Hart and Risley never said it didn’t. They pointed out that more talkative households moved beyond the “business language” of parenting—phrases like “stop that,” “put on your coat”—to something more responsive and engaging—“look at the pretty bird,” “what do you think of that?” Quantity is a proxy for quality because you need more words to ask questions and express interesting thoughts.

The good news is talking to children more is something every parent can do. And parents in every social class do, in fact, talk a lot to kids. Within a low-income Spanish speaking population, for example, Fernald found that while some parents spoke only 67 words to their 18-month old babies in an hour, others spoke as many as 1200 words.

Enter Dana Suskind. She first learned about the thirty-million-word gap in her work as a cochlear implant surgeon in Chicago. With her patients, she knew the difference that parent engagement made in helping a deaf child learn to speak and listen. And she realized that the patterns she saw among deaf families were true for all families. Although very few surgeons branch out into social science, Suskind felt compelled to found the Thirty Million Words Initiative to translate science into practice.

TMW, as the program is known, develops parent-directed curriculums that show mothers and fathers how much power they have over their children’s futures just by talking to them. Suskind sums up TMW’s approach with the mantra of the Three T’s: Tune In, Talk More, Take Turns. A study of the program’s effectiveness found that participants increased their knowledge about child development as well as the quantity and quality of their language.

Suskind’s book combines the story of how she came to this work with a clear accounting of the science behind it and of the efforts by her group and others to put it into practice. More than anything, though, Thirty Million Words is a call to arms. “If all parents, everywhere,” writes Suskind, “understood that a word spoken to a young child is not simply a word but a building block for that child’s brain, nurturing a stable, empathetic, intelligent adult, and had the support to make it happen, what a different world this would be.”

Parents and policymakers would do well to tune in.

Photos of Book Jacket and Dr. Dana Suskind: Dutton