I don't know much about IQ. In the most extreme case, of dissimilar education, the different was about 15 points. Is that a lot? What does that mean to laypeople?

As a parent of identical twins watching them develop and grow is fascinating. I do wonder at times how much of it is due to going through every single life stage together but then again there are times where that bond seems to go beyond environment. There was a sobering but very interesting documentary on identical twins called Three Identical Strangers, if you are interested in this type of stuff it's a good watch.

Is there a 'teaching the test' element to this? Does more exposure to education increase your ability to take a standardized test?

An interesting tidbit in the nature vs. nurture debate is that nature and nurture interplay in ways you might not expect. For instance, height is approximately 90% heritable in the United States -- but this does not mean that in a vacuum height is mostly genetic. It means that in the United States nutrition has mostly been solved (and yes, even the "food insecure" in the US rarely lack for the actual calories which would impact their height -- food insecurity causes other problems) and therefore the only real differences that can remain are the genetic differences.

It might be useful to look at any twin study through this lens; if we know for sure the genes are the same and nature is off the table, how much variance remains?

  - Genetics (DNA seq)
  - Epigentics (Histone acetylation, base methylation etc)
  - Brain wiring from experiences
  - Chemical impact from experiences, e.g. nutrition, toxins, sunlight, muscle dev etc etc.

> Of the 87 pairs, 52 experienced a similar type and duration of schooling within a similar location. In fact, 25 of these pairs attended the same school for some period of time. Analysis revealed that ‘Educationally Similar’ TRA pairs have an ICC of 0.87 ± 0.02 (n = 52)

So this study has 87-52-25=10 data points? Am I reading this correctly? Quite the reach to conclude what the article claims, if so.

IQ testing was recently found to be highly driven by response to difficult challenges, and could be influenced significantly by just tuning the rewards for participants doing well. Which suggests that measuring iq is a pretty fraught science, if you are trying to draw conclusions about heritable intelligence...

https://pmc.ncbi.nlm.nih.gov/articles/PMC10990577/

Sooo... yeah, but its not what you think.

There are two different kinds of IQ tests: convergent and divergent. Convergent tests are more common and test either knowledge or pattern matching. These tests are called convergent because they are a center of truth and conformance to that truth is the measured performance criteria.

Divergent tests measure the individual's creativity and abstract reasoning. The source of truth is the quantity of diversity of results submitted by the participant.

The implicit success criteria for convergent testing is reading comprehension. A person with dyslexia, for example, will perform worse on these tests irrespective of their learning speed, learned knowledge, intellectual curiosity, or creativity. This is a form of bias. Other forms of bias include memorization of terms, such as SAT preparation.

To further complicate things these measures typically only account for academic intelligence. Other forms of intelligence include social intelligence, spatial intelligence, creativity, conscientiousness, and so forth. In the concept of multi-dimensional intelligence, which is what is actually addressed in practice in the real world after high school, academic intelligence alone has very little benefit. Its like height in basketball where after 6.5ft all other factors become more important for all participants.