I wonder why a tiger-mom can send their kid to one hour of Sylvan tutoring a day and they get ahead, yet half of the town here sends their kid to school tutoring an hour after school every day and they can barely keep up? Is it because the tiger moms tutor their brightest kids and oour school only tutors the struggling students? I'm not even sure tracking is enough. I read here that the best educational fit would be to give the kids MAP testing (out of level achievement test) and group kids with a similar score in the same class for each subject, disregarding the ages:grade levels completely.
My homespun opinion agrees 100% with yours made in uk, if they would quit priotising socialization skills in school and start prioritizing education, plement tracking so that all students can learn enough during the eight hours a day they're already there, it would do more to "level the playing field".

Youth lives by personality, age lives by calculation. -- Aristotle on a calendar