Apparently my definition of tutor is so demanding that it should not be expected at all from a tutor (even if provided with information on the tutees weaknesses, tutors don't use the information effectively). However, the point of these studies are to gauge large scale effects rather than high variance small sample size effects. There's a lot more that is very interesting.
Hmm, it might be better to just go straight to what leading countries currently do (Finland/Estonia/Japan/Singapore/etc). Other factors probably play a bigger role, like school funding, school autonomy, teacher professionalism (high education level + continuing education + good pay), free school meals/healthcare/transportation etc
One major limitation is the cost. It costs lots of money to train teachers and pay them good salaries. What leading countries are doing currently might not be sustainable for the long run. Cognitive abilities also different greatly from people to people in different discipline. There is no silver bullet.
America is like a trust fund baby given all the advantages and then the baby goes "fuck it, life is too hard, I am just going to do coke and die early”.
The long term sustainability in at least one of those leading countries (Japan) has been shown effective for at least the period from the end of WWII to now. The principle difficulty they have is not maintaining high levels of educational success but in having enough children to keep the schools open and the teachers fully employed. But, that is a different concern than successful educational outcomes.
The average level of capability and comprehension in fundamental disciplines for students completing primary is a direct result of some fundamental differences in the way they approach classroom organization: for one middle school and high school students do not change classrooms during a school day.
Teachers rotate rooms while students remain in place and this maintains a less disjointed, less distracted transition between classes. There are still very little to zero technological advances to the teaching methods: blackboards/whiteboards, overhead projectors, hand written paperwork, textbooks.
The reasoning is simple. The fundamentals which students in primary education are in need of learning do not change much. Last years' textbooks are perfectly useful and the cost of replacement is directly carried by each student. If they damage a book, they must replace it.
Salaries for teachers are not unusually high, but they are also not low. The building and administrative costs are kept low, for one, by there not being a significant non-instructor labor expense of janitorial and maintenance workers. Schools share the pool of municipal HVAC and other trades for serious infrastructure, but janitors? Nope. The students are required to actually clean up after themselves, and to actually clean the whole school. It makes a difference, and those avoidable labor costs can be directed to proper compensation for the teaching staff.
Anecdotal observation of the overall efficacy of this approach reaches areas not usually measured as 'educational success' but also includes one noteworthy artifact. The common clerk, shop keeper, cook, or gas tank delivery driver all know that i = sqrt(-1) and that a complex number is a pair of numbers, one of which is the coefficient of (i). Let that sink in. How many people graduate with a B.A. from western schools without that?
There is not a 'silver bullet' but there are a full compliment of approaches which when applied together, consistently, and persistently, yield excellent sustainable outcomes.
Back to the falling population problem. There are pluses and minuses from the choice to provide separate boys and girls middle and high schools; one of which is lower teenage pregnancy and it's inverse, lower adult birthrates. (It's not the only reason for the lower birthrates, but it's not having zero impact.) You cant win 'em all.