also even at 12% that is a lot to play with. I am genuinely happy if I find a process in my own research that accounts for that much variance. Again it should be kept in mind that there are moderators at play that can lead to different results. For instance there is research which suggests environment plays a much larger role in disadvantaged groups than it does in high to middle-class groups. Likewise in relation to special education I think the goal is to help individuals reach their potential and take advantage of the variance that is available for improvement. Indeed, special education is probably a difficult example as it is not only genetic disorders but environmental ones, and yet in these cases the environmental damage caused by a variety of causes maybe more difficult to intervene in than genetic based disabilities. Then there are also other problems we have no idea whether they are genetic or not.
I agree that it is important to take the results seriously but given the importance for policy here I think it is also central to understand the role that moderators play and also not to underplay how meaningful even small amounts of variance can play.
You also have to wonder how much money we spend trying to correct social issues that may have a sizable cause rooted in genetics. Recognizing what you can and can not change could result in huge financial savings, but it could also impact certain professions greatly. Maybe to the point where they are willing to twist results to protect their livelihood?
The possibility is there sure but this also ensures strong and robust critical reviews. Indeed some are now starting to question the methodology used to calculate the percentage of variance ascribed to different causes and such critics are more likely than not to strengthen the methodology and as a consequence the accuracy of the results.