I'm not sure at the end of the day there's such a thing as 'intelligence', in terms of how we talk about it, like some sort of RPG stat. In my experience, kids aren't really 'smarter' than other kids, they have learning styles and brain patterns that match up with how the courses are run.

Anecdotes, I know, but I was terrible at math compared to the kids in high school who could all just memorize and regurgitate (I have ADHD & very poor working memory, and no random-access). These kids also regularly looked up answers to future quizzes they found online and bsed their way through. But, in college, which involves a more abstract and rigorous (and dare I say meaningful) understanding of the material, I excelled while many of my former colleagues fell behind as these were 'new problems' they couldn't just look up because they didn't have answers.

My point is intelligence is not a scalar axis in which some people are 'gifted' and some people are not, it's a multidimensional series of mental configurations that must be adapted to in the classroom and outside. Hire better teachers and pay them more is the only concrete thing I can think of. Gifted programs aren't the way as they're entirely arbitrary to a specific environment. The wrong teacher for the right student will ultimately make the student worse for it, and these programs don't account for how truly uninspired some teachers can be. Not to mention parents, or availability of learning materials, quality of libraries, etc etc.