For children who are still growing physically and mentally, both height and intellectual development are correlated with age, aren't they?. In an analysis where you are treating children who actually have a range of ages as a single age (i.e. "5th graders") finding some correlation between height and intellectual development isn't that surprising. It is just an expression of the underlying correlation between their age and intellectual development.
Height is generally correlated with IQ, though not very strongly (r = 0.2), and IQ is very strongly correlated with education success. It is also known that this correlation is not spurious: half of it is pleiotropy, which is, some of the genes that cause taller height also cause higher intelligence, and half of it is due to assortative mating, meaning taller people tend to have children with other taller people, so if pleiotropy causes taller people to be more intelligent, the tendency to marry taller people additionally amplifies the correlation.
Keep in mind though that the correlation, while very highly statistically significant and replicated over many data sets, is not very strong: at r = 0.2, the r^2 is 0.04, so only 4% of variance in intelligence is explained by height. Thus, it is not clear whether the height-IQ correlation plays significant role as a confounder in the study above.
But the numbers you describe are for adult height, right? Wouldn't you expect a much stronger effect if your sample was a mix of (say) 4-6th-grade kids. I think that's what GP is saying.
No, this is also found in children. See e.g. this[1] study, which also by design (it's a twin study) rules out the hypothesis that the effect is mostly environmental.
Thanks. That there is signal in which twin is taller at precisely age 12 is interesting, and seems like the same phenomenon as the adult effects.
But I'm saying something much simpler. In a school class, there's another effect, that the oldest may be a year or more older than the youngest. The mix of ages in a classroom will produce a correlation all by itself. It seems to me this would be a much bigger effect: 7th-graders are quite a bit taller, and better on tests, than 6th-graders.
Kids do not grow in lock-step. I.e., kids who will have exactly the same height as adults will have (probably considerably) different heights at the same age while growing up.
Given that, i doubt height measured at any one (age)point during childhood strongly correlates with iq. You'd need sufficient data to be able to reliably predict height as an adult for that, would be my guess.
I wonder if there is actually any correlation between height and IQ among otherwise healthy adults. There are developmental diseases, as well as malnutrition, which simultaneously lead to both smaller stature and lower IQ. All of the problems that I can think of which lead to above average height don't really affect IQ(acromegaly, marfan syndrome, etc).
You'll be extremely confused if you only think about very specific developmental disorders. That's not how highly polygenic traits like height and IQ work in general population. Some people are taller than others, and some people have higher IQ than others, and, to our best knowledge, this within population (or really, within cohort) variation overwhelmingly is not due to developmental disorders or environmental setbacks like e.g. malnutrition (though at the extreme levels, severe malnutrition or very debilitating disorders can and do have significant effects), but rather due to lucky draw of beneficial gene variants from the parents. As it turns out, some of the beneficial variants for height are also beneficial for IQ, this is called pleiotropy.
More directly to your question, yes, as I said in my previous comment, the effect is very real, and is not driven by some outliers. There have been dozens studies on this, with Ns in tens of thousands. Wikipedia has a sample of them: https://en.wikipedia.org/wiki/Height_and_intelligence
Interesting interpretation of the data. It would proably lead to the same conclusion though, that teachers are being rewarded for having naturally smarter/more developed students rather than their own performance.
I was always held back by the identity politics of age. Too smart in classes. To tall and lanky at sports. Growing up was a horrible time for me. Now, thankfully, decades later I excel at everything.
