When the 82-year-old psychologist Peter Gray describes the way he grew up, he punctuates the anecdotes by saying that modern parents would be arrested for letting a child have such fun. When he was 4 years old, he would walk to a store in Minneapolis to buy cigarettes for his grandmother. When he was 11, he would sometimes stay home from school in Hill City, Minnesota, to operate a newspaper printing press owned by his mother and stepfather.His parents were not arrested, and that’s because the childhood they permitted him to have was basically normal at the time, even if his family did have a newspaper printing press in the house. As a boy, Peter was obsessed with fishing and baseball; neighborhood friends taught him how to ride his bike and catch grasshoppers. Although Gray’s career as a scientist would begin with laboratory studies of rat hormones, he eventually found his way to writing about his childhood, in a fashion. Over the course of his 30 years in the psychology department at Boston College, he mixed principles of biology and anthropology to put together an evolutionary theory of play.Gray’s academic work defines play as a self-directed activity done only for its own sake. This, he came to believe, enables kids to figure out how to solve their own problems, nurture their own relationships, make their own rules, and manage their own disappointments. But he says that our society has spent the past 70 years or so interfering with that process. We’ve made it harder and harder for kids to do anything: They’re kept indoors for greater portions of the day and given less unstructured time; they play organized sports supervised by adults; they don’t go anywhere alone. Gray grew certain that this loss of independence has been harmful to their mental health.Gray’s theory, which he laid out in a 2013 book called Free to Learn, quickly found a welcome audience. The book was celebrated by advocates of free-range parenting and won endorsement from academic luminaries such as Steven Pinker. When Gray’s fellow psychologist Jonathan Haidt and his co-author Greg Lukianoff published their 2018 best seller on the threat of safetyism, The Coddling of the American Mind, they used the title of Gray’s popular TEDx talk “The Decline of Play” as a chapter header. Haidt, who is an Atlantic contributor, told me that Gray was “the star academic” in the section of his book that deals with play. “I wish every school in America could hear a talk by Peter Gray,” he said.Only recently has Gray expanded his idea in a way that is not quite so crowd-pleasing. Children’s need for unstructured play and exploration (guided by some safety rules and common sense) applies not just to vacant lots and city parks and backyards in the suburbs, he says, but to other settings too. It now extends to the wild spaces of the internet. “To grow up well, children have to be able to play in the world that they’re growing up in,” he told me when we spoke at his home in late winter. Kids should be free to play without their parents’ supervision, Gray insists, even when they go online.Gray has always been a playful academic. As a graduate student at Rockefeller University during the late 1960s, he once filled every mailbox at the school with a note proclaiming that neckties were no longer required in the dining hall because they stifled thought by cutting off circulation to the brain. But the turning point in his career came a decade later, when his son, Scott, took up the mantle of rebelling at his school. Gray and his now-late wife moved him to a nontraditional school in Framingham, Massachusetts, where children received no formal coursework and directed their own education.Scott thrived in his new environment, and Gray, who saw how much happier and more engaged his son became, pivoted from doing lab experiments on rats to making more philosophical explorations of play and learning. He also studied his son’s new school, publishing survey data on the careers and lives of its alumni, as well as detailed observations of how its students played.Eventually, Gray would have enough of structured academia himself. By 2002, he’d made sufficient money off of a well-regarded psychology textbook that he was able to resign from Boston College and live comfortably in the small town of Millis, Massachusetts. The back of the wood-paneled house that he shares with his second wife is made entirely of glass, providing a broad view of the Charles River. By his account, his retirement has been as idyllic as his childhood. Gray sometimes kayaks against the current, up the river, for exercise.When I visited him on a frigid day in March, he was wearing the uniform of a practical person—simple shoes, navy trousers, light layers topped with a grandpa cardigan. David Sloan Wilson, an evolutionary biologist and friend of Gray’s who is a professor emeritus at Binghamton University, described him to me as an old man with a “very boyish look.” I would say he is more like a child’s drawing of a nice old man: pure-white hair, a reedy frame, smile lines.Wilson also described his friend as a pied piper, apparently intending this as a compliment. And from his riverside retreat, Gray has been involved in leading a movement. In 2017, he joined up with Haidt and two others to found the nonprofit Let Grow. The organization, which raised about $2 million in contributions in 2024, encourages parents and teachers to stop watching kids so intently, and tries to fight “neglect” laws that frame a lack of child supervision as criminal or reckless behavior. Let Grow has also developed a program called Play Club, through which schools can offer age-mixed free-play time when the kids (mostly) supervise themselves.Gray and Haidt both served on the group’s board of directors. They had a collegial relationship, even though there were some minor differences in approach and worldview. The first of those was on the subject of kids and video games: Gray thought that video games provided kids with fruitful ways to play without adult control and was adamant about their value; Haidt respected that position but wasn’t so sure. The two psychologists also disagreed, from time to time, on whether kids should be using social media. But these seemed, at first, like secondary issues.Then, in 2023, Haidt sent Gray a prepublication copy of his next book. The Anxious Generation: How the Great Rewiring of Childhood Is Causing an Epidemic of Mental Illness opens with an extended metaphor comparing smartphone and tablet use to a spine-melting trip to Mars, and goes on to make the case that personal technology has caused a full-scale youth-mental-health crisis. Its argument seemed to fit the moment: Children were reporting that they didn’t like how much time they spent on social media and didn’t feel like they were in control of their habits; some were truly suffering. The Anxious Generation gave them—and their parents—language to describe what was happening.[Read: End the phone-based childhood now]Haidt’s book went on to spend more than two years on the New York Times best-seller list. It was translated into dozens of languages and excerpted in this magazine. And the policies that it suggests, to remove smartphones from schools and bar kids younger than 16 from social media, quickly came to seem like obvious solutions. (In the past few years, they’ve been taken up by legislators in the United States and abroad.)But when Gray first read the manuscript in his lofted study overlooking the river, he was appalled. “The book frankly makes me mad,” he told me. “I have to say that. I think it’s unethical.” Although The Anxious Generation goes on at length about the benefits of free play, and even makes specific mention of Let Grow, its message overall was for Gray inimical to the nonprofit’s mission. As he sees it, the analysis improbably suggests that taking away phones would prompt kids to run around exploring as their grandparents had done. The few freedoms that kids had left were private communications with their friends and some independent movement, permitted only so long as they could be tracked and called. More than that, Haidt’s book implies that kids cannot be trusted to delve into the online world on their own, or even taught to do it safely. The internet is too dangerous for children—too full of scary strangers and powerful temptations—much in the same way that parents and pundits had decried the perils of the physical world generations before. Haidt had wanted feedback on the manuscript. Gray told him he disagreed with its premise.Months later, after the book came out, Gray stepped down from the Let Grow board so that the other members wouldn’t feel caught in the middle of a conflict. Then he posted a critique to his Substack. Gray wrote that he took “no pleasure” in rebutting his colleague’s work. “I have tried to avoid it but no longer can,” he wrote. “As a society we have almost a knee-jerk reaction to believe that the solution to any problem experienced by kids is to deprive them of yet one more freedom, and this book is helping to jerk some of those knees even further.”The two men haven’t spoken a word to each other since their falling-out. “Jonathan Haidt is a likable person,” Gray told me. “He’s polite. He’s generous.” Gray said he is a fan of Haidt’s previous work: “His strong point has always been kind of large, somewhat philosophical arguments based on general observations and a certain amount of evidence, and he’s very good at that.” But Gray viewed Haidt’s newest large, somewhat philosophical argument as not only incorrect but immoral.The first time we spoke, Gray referred to social-media age minimums as a violation of human rights. When we met in person, I asked him whether that was truly his position. He repeated that it was. Before The Anxious Generation was published, Gray had been working on another book about the broad topic of play. But he scrapped that one after posting his rebuttal, and instead began to write a full-length counterpoint to Haidt’s ideas for an imprint at Penguin Random House. That book, titled Restoring Childhood: How to Set Kids Free in the Age of Anxiety, is due to publish in September.The new book will argue that the mental-health crisis affecting children is real, but has nothing whatsoever to do with what Gray describes as the “moral panic” over smartphones and social media. The real problem, he says, has to do with schools—and in particular with the 2010 rollout of the Common Core standards, which narrowed teachers’ options for creative curricula and increased the amount of time that the average American student spent taking tests.To make that case, Gray points to the American Psychological Association’s annual Stress in America study, which surveyed kids in 2009, just before Common Core was introduced, and in 2013, just after. In 2009, 43 percent of U.S. teenagers said that performing well in school was a source of stress in their lives. In 2013, this number jumped to 83 percent. Gray found analogous survey data from before and after similar educational reforms in Sweden and England were put in place.[Read: The flip-phone cleanse]School policies were not the only things that changed from 2009 to 2013; smartphone use, for example, skyrocketed across the same few years. But lots of evidence affirms the notion that in America, at least, children are more stressed out by school than by any other aspect of their lives. Young people often say that they hate school, and youth suicides are far more common during the school year. In 2024, 68 percent of U.S. teenagers surveyed by Pew Research Center said that they felt a great deal or fair amount of pressure to get good grades—significantly more than those who said they felt pressure to look good or fit in. Studies of teens in North America and parts of Europe also suggest that school pressure has increased more for girls than it has for boys over the past two decades, which is consistent with the fact that, in some respects, the teen-mental-health crisis has been more intense for girls.Restoring Childhood goes on to make another, even more surprising argument: It says that computers and video games have actually been responsible for improving children’s mental health. Teen suicides rose in every decade from the 1950s through the 1980s, Gray writes, as restrictions were increased on children’s freedoms. Anxiety and depression seem to have been rising too. But that trend was temporarily reversed by the arrival of the digital world. Suddenly, kids had a new place where they could connect with one another, make their own rules, and solve their own problems. They were among the early adopters of the new technologies, and so became authorities in their households, giving them a chance to feel competent and helpful. Teen-suicide rates never went back down to the levels of the 1950s, but they did decline by about 40 percent from 1990 to 2010. “Everybody was ignoring that,” Gray said. “Nobody was writing about that.”Just two years ago, Penguin Random House put out The Anxious Generation. Now the publisher seems confident that people are ready for a counternarrative: Gray says that he received a $500,000 advance for his newest book. Wilson, the Binghamton professor and Gray’s friend, told me that he read the book in manuscript form and found himself convinced. “I want it to have the exact same exposure and impact as Jonathan’s book,” he said. “I would like it to be as splashy as it could be and to set up conversations at every level as to which of these interpretations is correct.”You will not be surprised to hear that Haidt has a very different reading of the evidence. When I asked him what he made of the claim that computers were actually a boon to children’s mental health from 1990 to 2010, he instead proposed that any improvement during that period might have resulted from the phasing out and banning of leaded gasoline. (Lead exposure has been tied to developmental disorders and mental-health problems.) As for Gray’s critique of his smartphone-and-social-media hypothesis, Haidt said that it was overly reliant on the dissenting opinion of what he characterized as a minority of researchers. In particular, he mentioned Candice Odgers, a psychology professor at UC Irvine, and Christopher Ferguson, a psychology professor at Stetson University.Gray does feature Odgers and Ferguson in Restoring Childhood, but these are not the only scholars who have taken issue with the science as presented in The Anxious Generation. I spoke with more than a dozen people who study technology and child development, and many expressed concern that Haidt overstates the strength of correlational findings and suggests causation where it hasn’t been proved. (A 2024 report on teenagers’ use of social media from the National Academies of Sciences, Engineering, and Medicine concludes that “the scientific literature on the health effects of social media use is mixed and inconclusive.”) Several of them also quibbled—as did Gray—with Haidt’s emphasis on controlled experiments that found people’s mental health improved after breaks from social media. They said these are flawed because participants consciously or subconsciously know the results that are expected of them. (Haidt, when I put this to him, replied: “If all you can say is, Well, maybe they could guess the hypothesis, then you basically are saying all psychological research is useless.”)[Read: What did people do before smartphones?]But if the quality of Haidt’s arguments and evidence is up for debate, the same is true of Gray’s. The dangers facing kids on social media, for instance—in an ecosystem that was specifically designed to capture their attention for profit—aren’t quite analogous to those they’d find offline. Or take the crucial data from the Stress in America surveys, which are presented in Restoring Childhood as a meaningful signal of the harmful effects of Common Core reforms. Reported levels of school stress did double from 2009 to 2013, according to that work, but the numbers roughly doubled for other common stressors, too, including family finances—so any school-related effect on stress does not appear to be unique. When I asked Gray about this issue, he said it had been “nagging” at him, and that he was going to add a footnote to the book about it before publication. I pointed out to him a few weeks later that the surveyors had also changed their methodology between 2009 and 2013. The phrasing of the questions had shifted; the first survey had asked respondents to select their top two stressors, but the second one asked them to assign scores to a list of possible stressors. Gray was caught off guard by this, and he went on to ask his publisher to adjust or remove any reference to the Stress in America surveys. That request arrived too late to change the print edition, but Gray said he plans to make the edit to the ebook and audiobook.Restoring Childhood does offer other lines of evidence, though. “I think there’s a reasonable hypothesis here,” Ferguson told me when I asked about Gray’s book, which he had read in advance, and blurbed. He said he thinks that focusing on schools as the source of children’s mental-health decline makes sense, but added that he would like to see more evidence that the school environment had gotten that much worse. “My memory of schools in the ’70s and ’80s was: They also sucked,” he said.Odgers, who also provided an endorsement for Restoring Childhood, told me that she appreciates the fact that the book is “broadening the conversation” about children’s mental health to include “a major stressor as reported by young people, that we actually see in the data.” But she expressed frustration at the logic used by Gray and Haidt alike. She noted their shared willingness to apply one explanation (video games, unleaded gas) to the mental-health improvements of the 1990s and 2000s, and then a completely different one (Common Core, social media) to a later section of the same trend line. No serious epidemiologist would reason in this way, she said. Both Gray and Haidt tended to downplay other obvious factors, such as the severe adult-mental-health crisis that unfolded during the same years. “Caregiver mental health is by far the strongest predictor of childhood mental health,” Odgers said.Pete Etchells, a professor of psychology and science communication at Bath Spa University, also pushed back on the idea that Common Core is the primary cause of mental-health problems among American kids. “This is a common trap that we fall into when trying to figure out what’s going on with those declines,” he told me. “We try to answer the question of ‘What one big thing can explain this?’ The answer, in my view, is that there isn’t one big thing.” This was generally the thesis of Etchells’s own book Unlocked: The Real Science of Screen Time (And How to Spend It Better), which came out the week before The Anxious Generation did, sold only a few thousand copies, and received hardly any attention at all.Come September, the fight over that “one big thing” will be renewed. Which change that happened 15 years ago was the real source of so much misery for children? “You can’t run experiments on history,” Haidt said, so we’ll never be able to prove that smartphones and social media caused the steep decline in youth mental health. “We just have to say which hypothesis is more plausible,” he said—and he’s yet to hear one more plausible than his own.When I met with Gray, he said that he has total confidence in his idea: “The evidence is really very overwhelming.” Later on, I tried to press the issue: Couldn’t there be some other factors in the mix? What if Common Core had been just one of many causes of the problem? “It would be nice” if there really weren’t any one big thing, he said, but he simply didn’t feel that this was the case. “So far, I haven’t heard of any other possibility that has the same plausibility.” He’d been studying the numbers and considering the alternatives, and he didn’t see how his theory could be wrong.