Here is a brief excerrpt from an artic le by Adam Grant for The New York Times. Dr. Grant, a contributing Opinion writer, is an organizational psychologist at the Wharton School of the University of Pennsylvania. This essay is adapted from his new book, “Hidden Potential.”

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Credit: Katy Freeman

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Which country has the best education system? Since 2000, every three years, 15-year-olds in dozens of countries have taken the Program for International Student Assessment — a standardized test of math, reading and science skills. On the inaugural test, which focused on reading, the top country came as a big surprise: tiny Finland. Finnish students claimed victory again in 2003 (when the focus was on math) and 2006 (when it was on science), all while spending about the same time on homework per week as the typical teenager in Shanghai does in a single day.

Just over a decade later, Europe had a new champion. Here, too, it wasn’t one of the usual suspects — not a big, wealthy country like Germany or Britain but the small underdog nation of Estonia. Since that time, experts have been searching for the secrets behind these countries’ educational excellence. They recently found one right here in the United States.

In North Carolina, economists examined data on several million elementary school students. They discovered a common pattern across about 7,000 classrooms that achieved significant gains in math and reading performance.

Those students didn’t have better teachers. They just happened to have the same teacher at least twice in different grades. A separate team of economists replicated the study with nearly a million elementary and middle schoolers in Indiana — and found the same results.

Every child has hidden potential. It’s easy to spot the ones who are already sparkling, but many students are uncut gems. When teachers stay with their students longer, they can see beyond the surface and recognize the brilliance beneath.

Instead of teaching a new cohort of students each year, teachers who practice “looping” move up a grade or more with their students. It can be a powerful tool. And unlike many other educational reforms, looping doesn’t cost a dime.

With more time to get to know each student personally, teachers gain a deeper grasp of the kids’ strengths and challenges. The teachers have more opportunities to tailor their instructional and emotional support to help all the students in the class reach their potential. They’re able to identify growth not only in peaks reached, but also in obstacles overcome. The nuanced knowledge they acquire about each student isn’t lost in the handoff to the next year’s teacher.

Finland and Estonia go even further. In both countries, it’s common for elementary schoolers to have the same teacher not just two years in a row but sometimes for up to six straight years. Instead of just specializing in their subjects, teachers also get to specialize in their students. Their role evolves from instructor to coach and mentor.

It didn’t occur to me until I read the research, but I was lucky to benefit from looping. My middle school piloted a program to keep students with the same two core teachers for all three years. When I struggled with spatial visualization in math, Mrs. Bohland didn’t question my aptitude. Having seen me ace a year of algebra, she knew I was an abstract thinker and taught me to use equations to identify the dimensions of shapes before drawing them in 3D. And after a few years of observing what fired me up in social studies and the humanities, Mrs. Minninger knew my interests well. She saw a common theme in my passions for analyzing character development in Greek mythology and anticipating counterarguments in mock trial — and suggested doing my year-end project on psychology. Thank you, Mama Minnie.

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Here is a direct link to the complete article.

Adam Grant, a contributing Opinion writer, is an organizational psychologist at the Wharton School of the University of Pennsylvania. He is the author of “Hidden Potential: The Science of Achieving Greater Things,” from which this article is adapted, and the host of the TED podcast “Re: Thinking.”