Another anecdote from Outliers:
Every four years, an international group of educators administers a mathematics and science test to elementary and junior high students around the world. (It’s sometimes referred to as the TIMMS.) When students sit down to take the TIMMS exam, they also have to fill out a lengthy questionnaire. This questionnaire asks about everything from their parents’ background to what their friends are like. It’s a very demanding exercise, so demanding that most students leave ten to twenty of the approximately 120 questions blank.
Here’s the kicker: if you rank each country by how many questions they answer on the questionaire and compare it to the rankings of the scores on the TIMMS, the rankings are exactly the same!
In other words, if you want to predict how well a country will do on the math exam, give them a task that measures how hard they are willing to work. It doesn’t even have to be math related. Students who stick with the demanding task are more likely to be successful on the exam.