[AndrewKemendo]

In general I agree with you that this is unrepresentative for a nation as a whole - see my other comment for that.

However one advantage of a sample like this is that significant independent variables like the ones you mentioned are widely held constant, which means that the evaluated variables will have a stronger power. So it is informative relative to others.

It would be best to take this study into context with other studies which compare educational achievement and poverty level.

[Bsharp]

Agree that there are other things this study may be beneficial for. I edited my initial comment to acknowledge that this study and its conclusions are probably being hyped by the media, and it's actual value and the limitations of the study may be addressed by the authors in the study.

Unfortunately, the authors' words will be replaced by journalists to get attention.