I think you can change one's IQ.

I recently stumbled upon a paper published last year that suggests that fluid intelligence can be trained and that the training effect is dosage-dependent:

Improving fluid intelligence with training on working memory Jaeggi et al. PNAS. 2008.

Fluid intelligence (Gf ) refers to the ability to reason and to solvenew problems independently of previously acquired knowledge. Gf is critical for a wide variety of cognitive tasks, and it isconsidered one of the most important factors in learning. More- over, Gf is closely related to professional and educational success, especially in complex and demanding environments. Although performance on tests of Gf can be improved through direct practice on the tests themselves, there is no evidence that training on any other regimen yields increased Gf in adults. Furthermore, there is a long history of research into cognitive training showing that, although performance on trained tasks can increase dramatically, transfer of this learning to other tasks remains poor. Here, we present evidence for transfer from training on a demanding working memory task to measures of Gf. This transfer results even though the trained task is entirely different from the intelligence test itself. Furthermore, we demonstrate that the extent of gain in intelligence critically depends on the amount of training: the more training, the more improvement in Gf. That is, the training effect is dosage-dependent. Thus, in contrast to many previous studies, we conclude that it is possible to improve Gf without practicing the testing tasks themselves, opening a wide range of applications.

Speaking of IQ, Linda S. Gottfredson recently published Logical fallacies used to dismiss the evidence on intelligence testing which might be of interest to some of the readers.

I agree that IQ is somewhat malleable, but I'm by no means confident that all attempts to raise IQ, e.g. test-taking skills, will reduce akrasia, or improve planning, or risk taking decisions.