"We're both very cautious," says Amy Thornborrow of herself and her husband. "He's actually more so." So when their son brought home a project from his Menlo Park, California, school asking students to do something on their own for the first time, she wasn't sure her husband would be up for it. But she took a chance and placed the information packet where he would see it. And then?

"He did a 180!" Thornborrow says. "He liked it so much that he cut out a little quote from it and put it on the kitchen cabinet."

That quote—"All the worry in the world doesn't prevent death. It prevents life"—sums up the philosophy of Free-Range Kids, the movement I founded after becoming fed up with how unnecessarily terrified we've become for our children. The crime rate today is lower than when most of us were growing up. Yet everywhere I go, I hear about parents who are so scared for their kids that they won't let them do anything on their own.

The Oak Knoll School in Menlo Park brought the Free-Range Kids Project, an optional, free, outside-the-classroom activity, to its K–5 students in 2014. Adapted from an assignment created by New York City public school sixth grade teacher Joanna Drusin, the rules were simple: Think of something you feel ready to do without an adult that, for one reason or another, you just haven't gotten around to yet. It could be walking the dog. Riding your bike to the park. Getting out of bed without making Mom beg. If their parents agree, the kids get cracking.

At Oak Knoll, where the theme that year just happened to be "confidence," about a third of the 700 students (and their parents) signed on.

The results were shocking. After a year of not letting their son ride his bike to school—too many cars!—Thornborrow and her husband allowed him to bike to a nearby friend's house on a Saturday, when traffic is lighter. The boy came home flushed and proud. His parents were even prouder. And just three days later, the husband said to Thornborrow unprompted, "Let's just let him go to school on his bike."

"He's been riding ever since," she says.

One little letting-go was all it took and poof! The joy crowded out the fear. For family after family, it was the same story, according to surveys Oak Knoll had parents and students fill out. One mom said it was "a lightbulb experience." Another called it "life changing."

For his project, Christine Keefer's third-grade son Jackson asked to get his hair cut on his own. Keefer was hesitant, but she said yes.

He came home with a mohawk.

Oh, how she hated that hairdo! But she also loved this new feeling of worrying less. A few days later she gave Jackson some money and asked him go get her a Coke. She was thrilled, she says, "because I could see how it's helping him grow." And he came back "just as giddy."

That new confidence allowed Keefer to make an even bigger leap—to stop managing Jackson's homework. Overseeing it had been "like an additional job during the day," the working mom told me during a follow-up conversation. "So just allowing myself not to check on his every move was sort of my Free-Range Project."

Her son didn't come home with all A-pluses. "But he did OK," she says, "and I could see he was much more proud of his grades than when I was micromanaging."

Oak Knoll has since made the project an annual event, complete with an assembly. "Now parents will come up to me and tell me other things their kids are trying," school counselor Nicole Scott says.

"From a policy standpoint, it's a great way to build community," says former mayor and current councilmember Peter Ohtaki. His own family did the project and now they too have started letting their 9-year-old bike to school himself.

Before this project, "as parents, when our kids asked permission to do something on their own," Oak Knoll Principal Kristen Gracia says, "we might have responded with a quick 'no.' Now I see us more likely to ask ourselves, 'Why not?'"

That's a question that opens up doors, minds, lives.