Teens in Shanghai spend 14 hours a week on homework, while students in Finland spend only three. And although there are some educational theorists who argue for reducing or abolishing homework, more homework seems to be helping students with test scores.

That’s according to a new report on data the Organization for Economic Cooperation and Development collected from countries and regions that participate in a standardized test to measure academic achievement for 15-year-olds, the Program for International Student Assessment (PISA).

Hours of Homework Assigned Weekly to 15-Year-Olds

OECD via Quartz

(It should be noted that while Shanghai scored highest on the 2012 PISA mathematics test, Shanghai is not representative of all of mainland China, and the city received criticism for only testing a subset of 15-year-olds to skew scores higher.)

While there are likely many other factors that contribute to student success, homework assigned can be an indicator of PISA test scores for individuals and individual schools, the report notes. In the individual schools in some regions—Hong Kong, Japan, Macao, and Singapore—that earned the highest math scores  in 2012, students saw an increase of 17 points or more per extra hour of homework.

The report also notes, however, that while individuals may benefit from homework, a school system’s overall performance relies more on other factors, such as instructional quality and how schools are organized.

On average, teachers assign 15-year-olds around the world about five hours of homework each week. But those average hours don’t necessarily tell the whole story. Across countries, students spending less time on homework aren’t necessarily studying less—in South Korea, for example, 15-year-olds spend about three hours on homework a week, but they spend an additional 1.4 hours per week with a personal tutor, and 3.6 hours in after-school classes, well above the OECD average for both, according to the OECD survey.

Within countries, the amount of time students spend on homework varies based on family income: Economically advantaged students spend an average of 1.6 hours more on homework per week than economically disadvantaged students. This might be because wealthier students are likely to have the resources for a quiet place to study at home, and may get more encouragement and emphasis on their studies from parents, writes Marilyn Achiron, editor for OECD’s Directorate for Education and Skills.

It should also be noted that this list only includes countries that take the PISA exam, which mostly consists of OECD member countries, and it also includes countries that are OECD partners with “enhanced engagement,” such as parts of China and Russia.