From the study:
Because we included children from both the Detroit and Ann Arbor metropolitan areas, we had a broad range of socioeconomic status, race, and ethnicity
Detroit has some of the worse public schools in the country and Ann Arbor some of the best. Yet, unless I missed it Jaeggi didn't breakdown any of the results by school location. Strange. I wonder which type of students were among those that she claimed benefited from the N-back?
Table 1's caption includes the line:
There were no significant group differences on any of the pretest measures or the demographic variables.
So presumably they didn't notice any correlations between the obvious demographic variables and performance.
Following up on the 2010 study, Jaeggi and University of Michigan people have run a Single N-back study on 60 or so children.
The abstract is confident and the mainstream coverage unquestioning of the basic claim. But reading it, the data did not seem very solid at all - I will forbear from describing my reservations exactly; I have been accused of being biased against n-backing, however, and I'd appreciate outside opinions, especially from people with expertise in the area.
(Background: Jaeggi 2011 in my DNB FAQ. Don't read it unless you can't render the above requested opinion, since it includes my criticisms.)