Flynn himself does not believe that the Flynn effect represented real intellectual gains. For any test, your grade is usually based on: * Your form on that day

Flynn himself does not believe that the Flynn effect represented real intellectual gains. For any test, your grade is usually based on: * Your form on that day (good day/bad day whatever) * Your competence * Test taking ability (TTA) The first one can result in pretty large fluctuations, though on the population level (what the Flynn effect measures) it should not matter. Competence usually means "knows the subject", for an IQ test this would (ideally) be "is smart". TTA is either "is prepared for the test" or "knows how to make educated guesses". It is believed that the Flynn effect largely results from two factors: * Some parts of the population were severely malnourished 50-100 years ago which hindered their brain development. * Improved TTA The first one would be a real gain (of intelligence), though with limited capability to expand upon, as these days almost no one (in US/Europe at least) is malnourished enough to allow for further gains at the population level The second is not a gain of intelligence though it is a gain of competence, just not the kind that we want to measure with an IQ test. As there are not many reasons to believe, that the current decline is due to nourishment/TTA, it may be that those are constant but actual intelligence is on decline.