Alright, I could not find the exact study I had in mind, but did come across a summary of the history of research in this area, which touches on what I was talk

Alright, I could not find the exact study I had in mind, but did come across a summary of the history of research in this area, which touches on what I was talking about: THIRTY YEARS OF RESEARCH ON RACE DIFFERENCES IN COGNITIVE ABILITY http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.186.102&rep=rep1&type=pdf http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.186... See around pages 240-243, Section 3: Mean Race–IQ Differences: A Global Perspective > Many critics claim that Western-developed IQ tests are not valid for groups as culturally different as sub-Saharan Africans (e.g., Nell, 2000). The main evidence to support a claim of external bias would be if the test failed to predict performance for Africans. Even if tests only underpredicted performance for Africans compared with non-Africans, it would suggest that their test scores underestimated their “true” IQ scores. However, a review by Kendall, Verster, and von Mollendorf (1988) showed that test scores for Africans have about equal predictive validity as those for non-Africans (e.g., 0.20 to 0.50 for students’ school grades and for employees’ job performance). The review also showed that many of the factors that influence scores in Africans are the same as those for Whites (e.g., coming from an urban vs. a rural environment; being a science rather than an arts student; having had practice on the tests; and the well-documented curvilinear relationship with age). Similarly, Sternberg et al.’s (2001) study of Kenyan 12- to 15-year-olds found that IQ scores predicted school grades, with a mean r
.40 (p .001; after controlling for age and socioeconomic status [SES], r
.28, p .01). In Rushton et al.’s (2003) study of African and non-African engineering students at the University of the Witwatersrand, scores on the Advanced Progressive Matrices correlated with scores on the Standard Progressive Matrices measured 3 months earlier (.60 for Africans; .70 for non-Africans) and with end-of-year exam marks measured 3 months later (.34 for Africans; .28 for non-Africans). Figure 1 shows the regression of exam marks on test scores for these university students.