The best way to improve schools? Invest in teachers.

Enter the quality-adjusted year of learning. The idea is to look at how much a student learns in a year of education at a high-quality educational program (such as Singapore’s schools). Then, other interventions can be benchmarked by how many months or years a student would need to spend in a high-quality educational environment to learn the same amount.

“Learning-adjusted years of schooling translates gains into a format that is more accessible to policymakers,” David Evans, one of the co-authors of the paper, told me.