Members of the royal family aren't often told what they can and can't do. But just a few days into his first year of school, 4-year-old Prince George already faces a mandate: No best friends allowed.

Thomas's Battersea, the school George attends, bans kids from having best friends, Marie Claire reports. Instead, teachers encourage all students to form bonds with one another to avoid creating feelings of exclusions among those without best friends.

Jane Moore, a parent whose child attends the school, explained the idea on a recent episode of the British talk show "Loose Women." "There's a policy," she said, "that if your child is having a party — unless every child is invited — you don't give out the invites in class."

The trend of banning best friends has been growing for several years, and it's spread beyond European borders to American schools as well. Some psychologists and parents argue kids become more well-adjusted when they have larger friend groups and can avoid negative feelings associated with feeling left out.

Critics, however, say the approach robs kids of the chance to form valuable coping skills. By grappling with mild social exclusion when they're young, kids will emerge as more capable, resilient adults, these advocates argue.

People who support kids having larger friend groups in place of best friends tend to view these larger groups as healthier for nurturing a sense of belonging. "We try to talk to kids and work with them to get them to have big groups of friends and not be so possessive about friends," Christine Laycob, director of counseling at Mary Institute in St. Louis, told the New York Times.

Best friends, with their tight bonds and inside jokes, throw a wrench into that open environment, school officials contend.

In England, where the trend is still more popular, schools across South West London, Kingston, and Surrey have taken up the practice. Some accounts suggest the practice has moved up north to Canada, as teachers in big schools may shuffle friendships around to expose kids to a range of peers.

A wealth of research indicates best friends create value for people throughout their lives. One study recently published in Child Development found people with best friends enjoyed better mental health well into adulthood.

"We weren't surprised that better adolescent close friendships turned out to be important, but we were surprised by just how important they turned out to be into adulthood," Rachel Narr, University of Virginia doctoral student and lead author of the study, told New York Magazine.

Narr's study also found kids with broader friend groups tended to grow up with higher rates of social anxiety than kids with smaller numbers of closer friends.

And although anti-best-friend policies may help kids in the short-term, research suggests the strong connections found among best friends could be vital for mental health in a world where adolescents are lonelier than ever.