IQ tests are notoriously hard to make. And they don't measure IQ, so much as what the tester considers IQ.

An amusing story. There was an IQ comparisson between rural and urban areas and the finding was that people in rural areas do worse on IQ test. But one psychologist thought that this can't be true.

So he went back to test and realized that IQ test that were given to rural/urban areas were same. The people from rural areas did worse on the written part of exams, because the rural areas lacked schools and children started learning/reading much later. Once he went back and revised the tests, removing most of test that had to do with reading and generally type of thought that rural children have less encounter.

Conclusion - the old IQ test didn't measure intelligence, unless you can increase intelligence by going to a better school, in which case, that isn't intelligence but knowledge.