I can tell you the reason in two words: NO DISCIPLINE!
“But IQ is supposed to be mainly about nature, not nurture.”
What government grant covered this study?
IQ, short for intelligence quotient, is a measure of a person’s reasoning ability. In short, it is supposed to gauge how well someone can use information and logic to answer questions or make predictions. They measure how well people can solve puzzles by recalling information they’ve heard. Every student can learn, no matter how intelligent, if the teaching capacity and program directives are workable.
IQ is about learning. Learning is about teaching and topic. If you dumb down people for 2 or 3 generations, the IQ does go down. But the capacity doesn’t. The mind becomes a starving animal. And it stops living without fuel. So it they teach nothing, the student learns at the same level. And is able at some point to provide nothing for survival it never got. They become clay.
wy69