For lower middle-income countries, potential economic gains from ensuring that all 15-year-olds attain at least the PISA baseline level of proficiency in reading, mathematics and science are estimated at 13 times their current GDP, on average, 28% higher GDP over the next 80 years. For upper middle-income countries, which generally show better learning outcomes, the gains would average 16% higher GDP over the same period. In other words, the gains from tackling low performance not only dwarf any conceivable cost of improvement - but also improve people’s well-being and stimulate economic growth.