What is the basic purpose of IQ tests?

Brigid: Why is it that some children perform much better than others at school?
Kellerman: Obviously, certain children are brighter than others, but it’s not as simple as that. A lot of emphasis is placed on intelligence measured by tests.
Brigid: The so-called IQ tests?
Kellerman: Yes, Basically they are intended to test linguistic and numerical skills, so some children are bound to suffer. This is very unfortunate. A child with an average IQ may turn out to be successful when he grows up.
Brigid: What you’ re saying is that some children have abilities that are not easy to measure, that aren’t appreciated.
Kellerman: Precisely. And if these skills are not spotted sufficiently early, they cannot be developed. That’s why, in my view, there are so many unhappy adults in this world. They are not doing the things they are best at.
Brigid: I see.
Kellennan: But at school, only those children who are good with words and numbers can do well in school examinations.
Brigid: Right. Is there anything a parent can do to help in this case?
Kellerman: Yes. In my opinion, a child should be judged on his individual talents. After all, being happy in life is put ting your skills to good use, no matter what they are.