The American Time Use Survey is valuable dataset operated by the Bureau of Labor Statistics. Each year it asks a large, representative sample of Americans to keep time-diaries, writing down exactly what they do during the day.
I am going to rely on time survey data to give us hints about PISA test-scores. PISA is taken only by those aged 15-year, but let's examine all kids aged 15-18, both to increase the sample size and because high-school is more important. I will only include 15-18 year olds who are enrolled full time in high-school.
I think the graph and the implications for educational outcomes are pretty self-explanatory, even though I will admit that I was (again) surprised by just how large the differences are.
The only thing I would like to caution is not to assume a 1-1 causal relationship between input and output: kids who are better at school anyway may also study more, getting a double-advantage so to speak.
This graph is worth keeping in mind next time you read that the Asian school system rather than Asian culture explains Asian educational outcomes. These are Asian-Americans under (largely) the same American public school system that the media has decided is the cause of Americas problems. With American teachers, American teacher unions, with typical American levels of education funding, and facing the same American lack of school choice.
The Asian school system was if I understand the history correctly originally a carbon-copy of western school systems. They may have retained more class-room discipline, and more memorization, but other than that there appears nothing magic about the schools themselves.
We have to look at the society outside the classroom if we want to explain the differences in outcome. Instead of mindlessly assuming all variation in output is due to education policy, one single input of the human capital production function.