That's not what the article is discussing (decline over time). We (all?) know white American have over average performance due to whatever reasons. The question is: Are they declining alongside the overall group. That might suggests that the reason(s) for this decline is cross-culture/ethnic/race.
(I'm not american) so I don't have a horse in this race.
These reports are becoming to find because measuring racial differences is considered racist, so you'd be asking for something that would not be acceptable in modern studies.
