One argument that IQ (here, we let that stand for whatever is measured, without making any supportive judgments that, or when and where it is an appropriate measure of something). Heritability of IQ is not-trivial, generally estimated to be around 80%. The remaining 20% is 'environment', and measurement error and the like.
Previous studies had shown the tremendous advantage that early exposure to language and complex concepts has on later development, and that means later school success, and that means higher IQ test achievement. Prior work showed that by age 3, children from privileged professional families had heard millions more words spoken than children from unpriviliged families. They also had heard many different words spoken and learned their use. Now, the NY Times reports that this difference can be detected even by or before age 2. Samples were small but the study reinforces the idea that very early experience is telling throughout later life.
Those who see important group differences in IQ are going to defend their viewpoint by saying that they know very well about environmental variation and take that into account but that early experiences cannot obscure the entire group difference. We don't happen to agree, and this is clearly a matter of personal politics all round, but there are a couple of questions that are fair to ask.
First, is it possible that the actual heritability of the measure is much lower than its estimates? If social class is correlated in families, say by neighborhood, race, or education etc., then this can inflate heritability estimates, showing similar values for similar reasons, in professional as well as lower SES families. This is why adoption studies are often used to show the true heritability, but even there there has been evidence of SES correlation in adoptions.
Secondly, if SES inequality were removed from the picture, the overall heritability might stay the same but there would be no difference of the average and far less variance (variation among individuals) among what were previously very different SES groups.
Third, education policy strives and presumably would strive even harder, to standardize what children are taught from birth on up. They'd be taught or exposed to what our society values, be it vocabulary or mathematics or music or sports. IQ test scores could increase steadily, as they have done for the past several decades, by making the most of everyone's inherited abilities.
There will always be those who are unusual on this or any other kind of value-score system. There will be those who are seriously impaired or seriously gifted, however the neural mechanism works. But the issues of group differences would largely if not entirely disappear; there will always be some average difference between any two groups that are compared on almost any measure of attributes, but that doesn't make the difference 'important', which is a social judgment.
The current study doesn't take us all the way back to Freudian ideas that the first glimpse an infant has of the world is hugely transformative, though who knows what further studies might find. In any case, the important fact is not about the IQ controversy, because there is no reason to doubt that an enriched environment throughout life is an enriching fact of life.