IQ does measure something related to the brain's cognitive ability. The debate is if it's measuring "intelligence" and what the definition of that is, not that

IQ does measure something related to the brain's cognitive ability. The debate is if it's measuring "intelligence" and what the definition of that is, not that it doesn't mean anything. IQ tests are highly reliable in that you generally get the same scores when you retest. A movement from one year to the next relative to the population at whole is significant.