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SAT scores were re-normed in ~1995 (officially), and possibly an upward drift was allowed thereafter (unofficially), so you can’t compare a specific score (1250, say) on a mid-80s SAT to 2023, without making adjustments.
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There has been SUBSTANTIAL grade inflation over the last few decades, so, again, you can’t readily compare a GPA from the 80s to today.
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Adjusting for the 2 facts above, there has probably been more sorting of high end students (90th+ percentile) into selective and highly selective (i.e. elite) institutions, as its easier for students further away from these schools to find out about them (the internet), travel to/from them (both as prospective students and as matriculated students), communicate with home, etc. Also, greater realization of the potential rewards of an elite education, greater scholarship dollars at elite schools, etc. And finally, the much higher % of Asian kids in the HS pool, with a culture that does, in fact, reflect the “tiger mom” stereotype some of the time, has helped move the bar higher.