Image Dramatic play, believed to improve cognitive self-control, is a central part of the Tools of the Mind curriculum. Credit... Gillian Laub for The New York Times

Bodrova and Leong had both studied Vygotsky, and they discussed whether some of his methods might help improve the climate of these classrooms. For Vygotsky, the real purpose of early-childhood education was not to learn content, like the letters of the alphabet or the names of shapes and colors and animals. The point was to learn how to think. When children enter preschool, Vygotsky wrote, they are “slaves to their environment,” unable to control their reactions or direct their interests, responding to whatever shiny objects are put in front of them. Accordingly, the most important goal of prekindergarten is to teach children how to master their thoughts. And the best way for children to do that, Vygotsky believed, especially at this early age, is to employ various tools, tricks and habits that train the mind to work at a higher level. So Tools of the Mind students learn to use “private speech” — to talk to themselves as they do a difficult task (like, say, forming the letter W), to help themselves remember what step comes next (down, up, down, up). They use “mediators”: physical objects that remind them how to do a particular task, like CD-size cards, one with a pair of lips and one with an ear, that signify whose turn it is to read aloud in Buddy Reading and whose turn it is to listen. But more than anything, they use play.

Most of Vygotsky’s counterparts in the field of child psychology, including influential figures like Jean Piaget and Maria Montessori, held that imaginary play was an immature form of expression, a preliminary stage of development. But Vygotsky maintained that at 4 or 5, a child’s ability to play creatively with other children was in fact a better gauge of her future academic success than any other indicator, including her vocabulary, her counting skills or her knowledge of the alphabet. Dramatic play, he said, was the training ground where children learned to regulate themselves, to conquer their own unruly minds. In the United States, we often associate play with freedom, but to Vygotsky, dramatic play was actually the arena where children’s actions were most tightly restricted. When a young boy is acting out the role of a daddy making breakfast, he is limited by all the rules of daddy-ness. Some of those limitations come from his playmates: if he starts acting like a baby (or a policeman or a dinosaur) in the middle of making breakfast, the other children will be sure to steer him back to the eggs and bacon. But even beyond that explicit peer pressure, Vygotsky would say, the child is guided by the basic principles of play. Make-believe isn’t as stimulating and satisfying — it simply isn’t as much fun — if you don’t stick to your role. And when children follow the rules of make-believe and push one another to follow those rules, he said, they develop important habits of self-control.

Bodrova and Leong drew on research conducted by some of Vygotsky’s followers that showed that children acting out a dramatic scene can control their impulses much better than they can in nonplay situations. In one experiment, 4-year-old children were first asked to stand still for as long as they could. They typically did not make it past a minute. But when the kids played a make-believe game in which they were guards at a factory, they were able to stand at attention for more than four minutes. In another experiment, prekindergarten-age children were asked to memorize a list of unrelated words. Then they played “grocery store” and were asked to memorize a similar list of words — this time, though, as a shopping list. In the play situation, on average, the children were able to remember twice as many words. Bodrova and Leong say they see the same effect in Tools of the Mind classrooms: when their students spend more time on dramatic play, not only does their level of self-control improve, but so do their language skills.

In the past, when psychologists (or parents or teachers or priests) tried to improve children’s self-control, they used the principles of behaviorism, reinforcing good and bad behaviors with rewards and punishments. The message to kids was that terrible things would happen if they didn’t control their impulses, and the role of adults, whether parents or preschool teachers, was to train children by praising them for their positive self-control (“Look at how well Cindy is sitting!”) and criticizing them for their lapses. And in most American prekindergartens and kindergartens, behaviorism, in some form, is still the dominant method. But Bodrova and Leong say that those “external reinforcement systems” create “other-directed regulation” — good behavior done not from some internal sense of control but for the approval of others, to avoid punishment and win praise and treats. And that, they say, is a kind of regulation that is not particularly valuable or lasting. Children learn only how to be obedient, how to follow orders, not how to understand and regulate their own impulses. The ultimate goal of Tools of the Mind is not emotional or physical self-regulation; it is cognitive self-regulation — not the ability to avoid grabbing a toy from the kid next to you (though that’s an important first step), but the much more subtle ability to avoid falling for a deceptively attractive wrong answer on a test or to concentrate on an arduous mental task. And those abilities are more difficult to affect by other-directed regulation. Because the abilities are more abstract, they are less likely to be elicited by rewards. Kids are rarely able to organize their thoughts better in order to get an ice-cream cone.

As a result, many practices that most prekindergarten teachers consider essential are more or less banned from Tools of the Mind classrooms. There are no gold stars, no telling the class that they are all going to have to wait until Jimmy is quiet; even timeouts are discouraged. When there is a conflict — when, say, Billy grabs a toy from Jamal — the Tools of the Mind teacher’s first questions are supposed to be: What was it in the classroom that made it hard for Billy to control himself? And what mediators could help him do better next time? The teacher does remind Billy that there is a rule and he broke it, but she doesn’t make a big deal out of the incident. “We pretty much try not to use this whole concept of misbehavior,” Bodrova told me. “These kids are not born criminals. Even if they do something that is completely out of bounds, they do it because they can’t stop themselves.”

There are not yet firm experimental data that prove that Tools of the Mind works. But two early studies that began in the late 1990s in Denver showed some promising results: After a year in the program, students did significantly better than a similar group on basic measures of literacy ability. And more recent studies, including one overseen by Adele Diamond, a professor at the University of British Columbia who is one of the most prominent researchers in the field of cognitive self-control, have shown that Tools students consistently score higher on tests requiring executive function. Angela Duckworth told me that when she read Diamond’s report, which was published in Science in 2007, “I got very excited.” Her failed 2003 study had persuaded her that the usual approach to self-control in early-childhood education, a brief intervention here or there, wouldn’t work. But Tools of the Mind was clearly a different strategy. “It’s an immersion approach,” she said. “It’s not that these kids are pulled out and they do self-control for half an hour a day. Everything is about self-regulation, every single moment. Everything about the culture that the classroom creates reinforces that.”