There’s an essay in the New York Times written by a mother whose identical twin daughters both saw their E.L.A scores sink by “approximately 40 points” between the fourth and sixth grades.
The essay, unfortunately, is completely devoid of any information to tell you what in god’s name she’s talking about. What does 40 points mean? 40 points on a test graded on a scale from 1 to 50 means something extremely different than 40 points on a test graded on a scale from 1 to 10,000.
Only after doing a lot of Googling did I finally figure out that in 2005, the NY English Language Arts scores for the eighth grade had a mean of 698.2 and a standard deviation of 32.41. So a drop of 40 points would exceed a standard deviation, and that’s a pretty large drop indeed.
Probably, everything happening here can be explained by HBD principles. First of all, because identical twins have identical genetic potential, when they are raised in the same environment they will get very similar test scores. In fact, even identical twins reared apart get very similar test scores.
The second thing going on is that tests given to younger children are much more susceptible to coaching because they cover a much narrower range of cognitive abilities. We see this with the Head Start program, which increases test scores for the young children who are in the program, but their scores eventually sink back to their genetic potential as they get older and the tests cover a broader range of cognitive abilities. Head Start only coached them to do well on the tests, it didn't make them smarter.
The evidence from the article is that her daughters were encouraged to read a heck of a lot, and that boosted their fourth-grade scores far above their genetic potential, but probably the sixth-grade test placed a much greater emphasis on reading comprehension and analysis and was more highly g-loaded, so the author’s daughter’s test scores regressed toward their genetic g.