The flaw in the reasoning should be obvious to anyone but a psychologist -- the test outcome becomes a self-fulfilling prophecy, rather than an unbiased predictor of future performance. The contempt for science among psychologists is shocking.
> so the consensus in psychometrics is that iq tests are not systematically biased against particular groups.
Psychologists also came to a consensus among themselves (and, as usual, without any scientific evidence) that Asperger's was a real mental illness, and that Recovered Memory Therapy was a real therapeutic method. Fortunately, and to some extent because of these credibility issues, society is in the midst of dumping psychology as a serious endeavor:
http://www.nimh.nih.gov/about/director/2013/transforming-dia...
In summary, until there is some science in brain research, all this talk about IQ testing is overreliant on effects without any clue about causes -- on descriptions without explanations.
Notice the name of President Obama's recently announced program -- the "Brain Initiative", not the "Mind Initiative". The handwriting is on the wall.