The story of how an introverted German scientist came to judge and counsel schools around the world is an improbable one. As a mediocre student in Hamburg, Schleicher did not particularly care about his classes—to the distress of his father, who was a professor of education. Later, at an alternative high school, teachers encouraged Schleicher’s fascination with science and math, and his grades improved. He finished at the top of his class, even winning a national science prize. At the University of Hamburg, Schleicher studied physics. He had no interest in his father’s field, considering it too soft. Then, out of curiosity, he sat in on a lecture by Thomas Neville Postlethwaite, who called himself an “educational scientist.” Schleicher was captivated. Here was a man who claimed he could analyze a soft subject in a hard way, much the way a physicist might study schools. At the time, 1986, the education establishment was dominated by tradition, theories, and ideology. “You had people dealing with every subject,” Schleicher tells me, “except looking at reality.”

Schleicher’s father did not approve. “His feeling was that you can’t measure what counts in education—the human qualities.” But Schleicher began collaborating with Postlethwaite anyway, creating the first international reading test.

Back then, countries subjected only small numbers of select students to such tests—or abstained from sampling altogether. “I remember everyone telling you, ‘We have the best education system in the world,’” Schleicher says. To his data-driven mind, this was madness. How can everyone be the best?

In April 1996, after Schleicher had joined the OECD, he and his colleagues pitched the idea of designing a smarter, more ambitious test than any that had preceded it—a way to shift the OECD from measuring inputs (like spending on schools) to outputs (how much kids learn). Many education ministers were skeptical, but Thomas Alexander, Schleicher’s boss, convinced them that their countries could not remain economically competitive unless they could measure what their students actually knew.

Ultimately, in the spring of 2000, nearly all 30 OECD members signed on, plus several other countries: 15-year-olds from 32 countries took the Programme for International Student Assessment (PISA). The exam tested more same-aged students in more developed countries than any other. And it measured not students’ retention of facts, but their readiness for “knowledge worker” jobs—their ability to think critically and solve real-world problems.

The results were so stunning that international newspapers leaked the rankings. The United States rang in somewhere above Greece and below Canada, a middling performance we’ve repeated every round since. To the astonishment of the Germans, who had believed their system among the best in the world, Germany ranked even lower.