Bad breeding.
New Math (late 1960s)
Word Attack (again 1960s)
TV instead of books (by 1960s everyone had a tv babysitter)
IQ Can Change Significantly During Adolescence
https://psychcentral.com/news/2011/10/21/iq-can-significantly-change-during-adolescence/30587.html
Correct. And that is the fault of modern medicine’s successes over opportunistic diseases. Where once the herd-culling transpired naturally, now faulty genetics intermingle and propagate. The saddest byproduct is we eliminate good humans through wars and foster more marginal humans through social welfare programs