EVERY three years the OECD, a club of mostly rich countries, tests hundreds of thousands of high-school pupils across the world on maths, reading and science. Its Programme for International Student Assessment (PISA) has become the leading benchmark for international educational comparisons, and has prompted policymakers to learn lessons from the best-performing school systems. The latest PISA study, conducted in 2015, assessed more than half a million students in 72 countries. For the first time, it also asked respondents in 53 countries broader questions about their social and emotional well-being, addressing their relationships with peers, parents and teachers. The findings, published on April 19th, suggest that students’ family circumstances and psychological well-being matter just as much as schooling does for their eventual performance.

One strong conclusion from the study is the importance of students’ desire to succeed, regardless of their natural aptitude. In general, the 25% of pupils describing themselves as the most motivated attain average test scores that correspond to an extra year’s worth of schooling relative to those of the bottom 25%. However, not all forms of motivation are equal.

The OECD distinguishes between external motivation, produced by pressure from others, and intrinsic motivation “sparked by an interest or enjoyment in the task itself”. Its study found that pupils who call themselves ambitious—which it describes as a proxy for self-driven effort—are less likely to say they feel anxious about a test than those who do not. Conversely, students who said they aspired to be one of the best students in their class—which the OECD interprets as being motivated primarily by their rank among peers—tended to report more anxiety than their less competitive classmates.

And anxiety, in turn, tends to reduce academic performance. Although a handful of places, notably Singapore, display strong test scores despite high levels of competitiveness and anxiety, most countries near the top of the anxiety scale, such as the Dominican Republic, had below-average results on the PISA science assessment. In contrast, those that displayed low levels of reported competitiveness and anxiety also had strong exam results, like the Netherlands and the Czech Republic. In the OECD’s words, motivation driven primarily by outsiders can lead to “disabling perfectionism”.