We like to focus on IQ because it is (theoretically, kind of) a constant. But few schools give cognitive assessments to every student, and teachers are not particularly good at recognizing when a student's cognitive ability is beyond what is expected of them in the classroom. That's partly because teachers are very good at training kids to keep their heads down and not make a fuss. Certain personality types are more likely to complain if the work they are given does not match their ability, and gender certainly plays a role.
Some parents do advocate for the children, but many parents do not realize that their child is gifted, and many assume that the schools know what's best for their children. Some schools provide a good array of services for gifted students. Some entire districts do not.
