Increasing fluid intelligence is possible after all

Almost 40 years ago, Jensen (1) claimed that, when all is said and done, there is not much one can do to raise people's IQs. Over the years, there have been various attempts to do so, which generally have yielded somewhat ambiguous results (2). Even successful attempts (3) have typically involved training people on the same kinds of items on which they would be tested, so that it was not clear whether the training was generalizable, rather than merely a result of practice effects on particular item types (4).