According to researchers, play reduces stress and makes children more socially competent—and evidence suggests that it does. But, perhaps more importantly, play supposedly improves working memory and self-regulation; in other words, it makes kids sharper and better-behaved. So, ironically, by shortchanging them on play in favor of academics, we may actually be inhibiting their development. Hirsh-Pasek, a psychology professor at Temple University, considers the move away from play to be a crisis, even comparing it to global warming, in the sense that it may take years for the consequences to be felt. When it comes to the value of play, she declares: "The science is clear."


Before tuberculosis claimed him, at just 37, Lev Vygotsky managed to produce a stack of volumes on topics as diverse as the psychology of art, the relationship between thought and language, the problem of consciousness, the behavior of primitive man, scientific language, and child development. While the amount of work he cranked out is notable in itself, what's more impressive is how influential that work has become, even though much of it remained unpublished and untranslated for decades following his death.But how clear is it? Even researchers who've devoted much of their careers to studying play question the more inflated claims of its importance. Within the world of those who take play seriously, there are multiple camps, each with its own dearly held tenets. There are the Free Players, who argue that play is a human right and that adults should more or less leave kids alone. There are the Play Skeptics, who see play as useful for blowing off steam but are dubious about its cognitive upside. And there are Play Moderates, who advocate a mix of free play, adult-guided play, and traditional classroom instruction. No matter whom you're talking with, though, it seems every discussion about play eventually comes around to a prolific Russian psychologist who died more than 75 years ago.

For play researchers, no one looms larger than Vygotsky, whose name, along with that of his longer-lived and better-known contemporary, Jean Piaget, pops up on seemingly every other page of the literature. Vygotsky viewed play, particularly pretend play, as a critical part of childhood, allowing a child, as he said in one oft-repeated quote, to stand "a head taller than himself." His biggest theoretical contribution may have been the Zone of Proximal Development: the idea that children are capable of a range of achievement during each stage of their lives. In the right environment, and with the right guidance (which was later dubbed "scaffolding"), children can perform at the top of that range.

For instance, Vygotsky explained, when a child can pretend that a broomstick is a horse, he or she is able to separate the object from the symbol. A broom is not a horse, but it's possible to call a broom a horse, and even to pretend to ride it. That ability to think abstractly is a huge mental leap forward, and play can make it happen.

Among the many who have been influenced by Vygotsky is Deborah J. Leong, the author, along with Elena Bodrova, of Tools of the Mind: The Vygotskian Approach to Early Childhood Education, an attempt to turn his theories into practical classroom techniques. Leong, a professor emerita of psychology at Metropolitan State College of Denver, points out that when young children are pretending, they often use bigger words than they normally would and fully inhabit their roles, like mini Method actors. If they're playing doctor, for instance, they might say "injection" or "thermometer." Recently she watched a group of preschoolers pretending to work at a well-known chain hardware store. "Welcome to Home Depot," a 4-year-old said. "You can do it, we can help." Meanwhile another group of children, who were pretending to be airport screeners, informed a would-be passenger that a bottle she was carrying was larger than the permitted three ounces.

Pretend play isn't just about vocabulary. A 2007 study published in Science looked at how 4- and 5-year-olds who were enrolled in a school that used the play-based, Vygotsky-inspired Tools of the Mind curriculum measured up to children in a more typical preschool. The students in the play-based school scored better on cognitive flexibility, self-control, and working memory—attributes of "executive function," which has been consistently linked to academic achievement. The results were so convincing that the experiment was halted earlier than planned so that children in the typical preschool could be switched to the Tools of the Mind curriculum. The authors conclude: "Although play is often thought frivolous, it may be essential."

With evidence like that, you might think that the kind of guided pretend play that Vygotsky favored would be universally embraced. In fact, according to Leong, it's fast disappearing, as the idea of learning becomes synonymous with memorization and standardized tests. Play is steadily losing out to what play proponents refer to as the "drill and kill" method. "We drill more because they can't pay attention, but they can't pay attention because they don't have these underlying play skills, so we drill more," Leong says. "It's pathetic."

Not to mention misguided, according to Kathy Hirsh-Pasek. Whether children play enough isn't an obscure debate among developmental psychologists. If it's true that children who spend too little time playing struggle with executive function, then we may be raising a generation of kids with less self-control, shorter attention spans, and poorer memory skills. If that really is the case, Hirsh-Pasek's talk about a crisis isn't so far-fetched.

She sees the Ultimate Block Party as the first step in a national effort to get people to stop dismissing play and start questioning the way we assume children learn. She wants to speak directly to parents, most of whom aren't poring over every issue of Child Development for the latest research on play. The goal, in a sound bite, is to take that research "into the streets, subways, and supermarkets."

It's not every day that an academic stages a spectacle in Central Park to bring attention to what is, honestly, a fairly small field of research. To pull it off, Hirsh-Pasek hired a public-relations agency and drummed up big-name corporate sponsors. There was a Sesame Street sing-a-long, what was billed as "New York's Largest Simon Says," and a Radio Disney Dance Party. A small company called Ridemakerz hawked its build-your-own remote-control cars. Not to mention the guy selling a nifty iPhone app that lets you play a technologically enhanced game of hide-and-seek using the smartphone's GPS capability.

There were also decidedly less-profit-driven booths, like the one run by the New York Coalition for Play. Rather than whiz-bang gadgets, they offered cardboard boxes and tubes, lots of fabric, ribbon, empty wine crates, and assorted items that would otherwise be found in a recycling bin. One of those overseeing the booth was Edward Miller, a senior researcher at the nonprofit group Alliance for Childhood, part of whose mission is to promote creative play. When asked what he thought of the Ridemakerz booth just a few yards away, he couldn't help rolling his eyes. "We're also concerned about the overcommercialization of play," he said. "The right answer is less programming and more opportunities for kids to make up things on their own."

Hirsh-Pasek is well aware that play purists look askance at including corporations in the pro-play campaign. Those who take a hard line on free play—that is, giving children basic materials like boxes and fabric and then leaving them alone—have zero use for Nickelodeon kid bands and pricey remote-control cars, which they see as just more ways for adults to get in the way. What she has in mind is a big tent, one that doesn't exclude fancy toys or snappy musical productions. Nor does she have much patience for advocates who claim that the only valuable play is the kind that doesn't involve anyone over 18. She wants kids to play on their own, sure, but she also wants them to engage in more guided play, where an adult or older child can take part.

There's research to back her up. A study she recently submitted for publication gave blocks to children divided into three groups. In one group, the blocks had already been assembled into a heliport. A second group was given blocks, and adults helped the children follow directions to build a heliport. A third group was given blocks and told to do whatever it wanted. The researchers then listened to the language children were using as they played. Those who were building a heliport with an adult used the most imaginative and spatial language (like "below," "on top," "next to"); the kids who were playing with the preassembled heliport used the least.

While she's no purist, Hirsh-Pasek is suspicious of some of the toys that purport to be educational. The title of Einstein Never Used Flashcards (subtitled How Our Children Really Learn—and Why They Need to Play More and Memorize Less) is an apparent slap at the Disney-owned Baby Einstein company. She also cites research that shows that electronic books for kids, the kind that talk and make noises, actually distract young readers: Kids who read them remember less of the narrative than kids who read the story on old-fashioned paper. What's more, Hirsh-Pasek says, she turned down millions of dollars from a corporate sponsor (which she declines to identify) that requested the right to name the Ultimate Block Party.

In many ways, she is placing herself in the middle. She's not trying to run toy companies out of business, but she is willing to criticize products that do more harm than good. She's not attempting to tear down traditional classroom education, but she is pushing hard for more play in schools obsessed with testing. To that end, she's working to make the research on play palatable for teachers and parents.

How good that research is, though, is a matter of debate. Peter K. Smith began studying play in the mid-1970s. At the time, he was a believer in the "play ethos," which he defines in his recent book, Children and Play, as the "very strong and unquestioned view of the importance of play." In that book, he quotes numerous researchers waxing enthusiastic about play's importance, asserting that it is "vital" and "the work of childhood" and "the supreme psychological need."

Later, Smith, a professor of psychology at the University of London, became a skeptic. "I looked at the textbooks of play" from Piaget forward, he says. "They said play is essential for development, that it enhanced this and this, and that and that, but they don't cite any evidence." So he decided to take a closer look. In the late 1980s, he picked a couple of studies that claimed to demonstrate the benefits of play. In one study, researchers had found that playing with small objects helped young children learn how to solve problems. Another showed that play made kids more creative. Smith replicated both using a double-blind procedure to eliminate any potential research bias.

His findings showed no difference in creativity or problem-solving ability between the kids who played and those who didn't. It was a setback for play advocates and made researchers wonder whether the field was based on science or sentimental hype.

More than two decades after Smith's debunking, researchers like Angeline Lillard, a professor of psychology at the University of Virginia, are still raising some of the same questions. "I think if you look hard at all the studies people cite as showing that play helps development, they are either correlation studies"—in other words, they don't prove that play actually causes cognitive gains—"or they have problems," she says.

Not that Lillard, or Smith, for that matter, is antiplay. Lillard is the author of the best-selling bookMontessori: The Science Behind the Genius and has written about the possible links between pretend play and social cognition. She does, however, believe that the field is in need of newer and better research. "My own view is that I would like for us to have firmer footing to stand on," she says.

But while scientific support for play can be overstated, sometimes the criticism of play can be unfounded. Last September, Time magazine published an article with the headline "Free Play Won't Make Your Child Smarter." The article was prompted by a study that looked at how 2,751 preschoolers fared in programs with a variety of approaches, including free play and traditional group instruction. That study concluded that "more quality instructional time" and "less free play time" would better prepare kids for school.

But the study's case against play in school isn't entirely persuasive. It's true that the kids who spent the largest chunk of their school day (41 percent) engaged in free play were behind their counterparts on skills like naming letters, naming numbers, and writing their names. But those who spent 29 percent of their time in teacher-guided play actually performed at the same level as the kids who played much less (only 13 to 15 percent of the time) when it came to naming numbers, highest number counted, language and literacy, word and letter identification, and writing their names legibly. In short, they played twice as much but learned the same amount. One of the authors of the report, Nina Chien, a postdoctoral researcher at the University of California at San Diego, acknowledges in an e-mail that this was proof "that kids can play a lot but still make good gains."

More interesting is what the researchers didn't test. Did the children who played more demonstrate higher levels of self-control and better working memory, as other research suggests they would? If so, did they outperform the kids—preschoolers, remember—who spent 15 percent or less of their time playing? Is being smart a race to see who can memorize the most, or is it about developing capacities to deal with a complex world?

While much of the research on play focuses on young children, the implications go well beyond third grade. In junior high, play is more likely to be called "discovery learning." When professors try to get college students to look up from their iPhones, it's probably referred to as "active engagement." But the principles are the same. Stuart Brown, one of the authors of Play: How It Shapes the Brain, Opens the Imagination, and Invigorates the Soul, has reviewed thousands of life histories and concluded that play is essential for children and adults. He's intent on spreading that gospel through his organization, the National Institute for Play, whose mission is to make human play a "credentialed discipline in the scientific community."

And it's not just people. That nonhuman primates engage in sophisticated play has been thoroughly established, and anyone who has dangled a string in front of a cat has conducted animal research. In his book The Genesis of Animal Play, Gordon Burghardt, a psychology professor at the University of Tennessee, reports playful behavior in lizards, turtles, and birds. Even fish have been known to amuse themselves.

For Hirsh-Pasek, the universality of play is part of the evidence of its value. Why would we do it if it didn't confer an evolutionary advantage? She concedes that some of the play research is more suggestive than slam-dunk, and that cleaner, stronger studies would be welcome. But she also argues that we already know enough to conclude that play matters, and that failing to preserve it in the lives of children could be a disaster.

She's doing her part to stave that off. Hirsh-Pasek says 40 cities have expressed interest in holding their own Ultimate Block Parties. She and her colleagues will soon unveil a Web site to promote play research, and more books are on the way. Their goal, she says, is to restore play to its rightful, respected place in the lives of children. "Even if we don't understand it perfectly, it's silly to take play away from society," she says. "It's like taking love away. It's crazy."