What exactly is an IQ score? An IQ score is derived from how well a person does on an exam measuring their "intelligence quotient." This exam consists of several different standardized tests and is justified as a scholarly way to gauge intelligence.
Over someone's adulthood, no matter how many times they take the IQ test, their scores are always consistent. This shows that the IQ test is extremely reliable in the sense of test-retest reliability.
IQ scores are associated with many important real-world behaviors outside the classroom and workplace too. They are associated with health-related outcomes including sickness and car accidents. IQ scores are also associated with crime, the lower the IQ score, the higher chance of criminal tendencies. The politics behind IQ scores hold true. There is barely any difference in the IQ scores of men and women. On the other hand, there is a huge difference in IQ scores in the sense of race. White people on average score 15 points more than black people do on IQ tests, but they do show substantial overlap.
The correlation between IQ scores and life achievements remains essentially identical even at extremely high levels of IQ, which doesn't make much sense to me because I feel as though Stephen W. Hawking and Albert Einstein have achieved so much more in their lifetime than a standard employee at a company.
Genetic and environmental influences on IQ are very consistent. Through family studies, IQ scores run fairly consistent, but we don't know whether it's for genetic reasons, environmental reasons, or both. Twin studies on the other hand have strongly suggested genetic influence.
In my opinion, IQ scores can be used to gauge intelligence to an extent. Test taking ability plays a huge role in IQ scores and just because someone gets a lower IQ score than me, I do not consider them any less intelligent than me.