Since the 1970s, the black-white IQ gap has dramatically shrunk on scholastic tests:
For example, on a scale where white 12th graders average 100, the reading scores of black 12th graders would have increased from IQ 80 in the 1970s to IQ 90 in recent years.
Meanwhile the math scores of black 12th graders have increased from IQ 82 in the 1970s to IQ 86 in recent years.
Assuming about a 0.67 correlation between reading and math skill from the 1970s to today, this suggests the composite scholastic black IQ has increased from IQ 79 in the 1970s to IQ 87 in recent years. A gain of 8 points! [Update Aug 17, 2017: the actual correlation is perhaps only 0.36, suggesting an even more dramatic gain of 9 points: from 77 to 86]
But on official adult IQ tests like the WAIS, the black-white IQ gap has been stable since the 1970s, and probably since the pre-Wechsler IQ tests of WWI.
When the Wechsler Adult Intelligence Scale (Revised) (WAIS-R) was normed in 1978, whites outscored blacks by 14.6 points (U.S. norms). By the time the WAIS-IV was normed in 2006, the gap was 15.7 points.
|white iq (u.s. norms)||black iq (u.s. norms)||white iq (white norms)||black iq (white norms)||black-white iq gap (u.s. norms)||black-white iqgap (white norms)|
|wais-r (1978)||101.4 (sd = 14.65)||86.8 (sd = 13.14)||100 (sd = 15)||85 (sd = 13.45)||14.6||15|
|wais-iii (1995)||102.6 (sd = 14.81)||89.1 (sd = 13.31)||100 (sd = 15)||86 (sd = 13.48)||13.5||14|
|wais-iv (2006)||103.4 (sd = 14)||87.7 (sd = 14.4)||100 (sd = 15)||83 (sd = 15.43)||15.7||17|
WAIS-IV U.S. norms from pg 27 (Table A1) of Black Americans Reduce the Racial IQ Gap: Evidence from Standardization Samples by William T. Dickens & James R. Flynn and from pg 190 of WAIS-IV, WMS-IV, and ACS: Advanced Clinical Interpretation edited by James A. Holdnack, Lisa Drozdick, Lawrence G. Weiss, Grant L. Iverson
What this suggests is that in past decades, scholastic tests underestimated the intelligence of blacks while official IQ tests have not. This is also consistent with the Minnesota transracial adoption study done in the 1970s, where blacks kids adopted into upper middle class white homes scored 10 IQ points higher than the black average on scholastic tests, but not at all above the black average on the WAIS-R.
Of course, this was not an apples to apples comparison of the gap on achievement tests and official IQ tests, since the scholastic data is from 12th graders while the WAIS data is from adults of all ages