Why I don't believe that playing basketball makes people tall? Because it's very difficult to do studies that isolate one variable without changing the other. [...] Use your head.
I linked you an article that detailed a meta-analysis of several IQ-education studies and you just wave it away with "it's difficult to do so I don't believe it"? What specifically is wrong with that study?
Or how about this one, showing how Norway's increase of compulsory schooling from 7 to 9 years in the 1960s bumped students' IQ scores?
The reason the overwhelming majority of scientists have concluded that IQ is mostly hereditary is due to identical twin studies. These studies are as close to being unbiased as one can reasonably hope to be. According to them, about 80% of IQ variance hereditary, irrespective of if the twins are living under the same household or not and irrespective of the inclusion of the age correlation on IQ.
Firstly, hereditary and genetic are not the same thing. I specifically mentioned the "stereotype threat" before to show how a cultural idea or stereotype can affect someone's measured IQ. This factor would come into play irrespective of whether twins have been reared inside the same family or not. Yet it's clearly not due to genetics.
This leads me to my second point, which is that evidence of in-group heritability does not necessarily prove that between-group variability is due to genetics. The Flynn effect is a clear example of when massive changes in IQ can happen to a population without any real difference in genetics.
So while I do think twin studies are a convincing argument for IQ having a large genetic basis (though, counterintuitively, it does seem like IQ and heritability may correlate with how 'culturally loaded' the test was, ie. the more cultural bias the greater correlation), everything taken together also makes me believe that under certain circumstances the environment can have an outsized influence as well. It seems to me to be extra prudent to keep this in mind when comparing populations of different socioeconomic standards and culture. For instance, there are indications that the prenatal environment is very important for brain development. Perhaps we don't have to go as far as malnutrition for food to become a very important factor? Incidentally this is also something which most twin studies have difficulty picking up.
Adoption studies by the way 100% show that IQ is inherited, how about you double check your claims.
How about you check the link I gave and tell me why it's bad?