I'm suggesting that you have to be within the top 5% class GPA to get in. So, some students may actually have a lower GPA, but still have a chance to get in, because they were in the top 5% of their class.
I'm also saying that students don't have to have the resources to take SAT prep courses, because they would only have to do well at their own schools.
If the public or private school was not accredited for possible acceptance into an Ivy League school, parents should know that and be able to do something about it, and so should the state or county.
But more importantly, poorly performing schools need to be identified and fixed. If they can't be, then it needs to be obvious that they are not able to prepare students for elite education.
It is not right for only those from wealthy families to be the only ones that can be adequately prepared, because they can go to prep schools and train for and retake standardized tests.
I think most districts in the U.S. have similar processes to attend an alternate school, but barriers remain high in low-income areas, ranging from stigma to logistics (e.g., transportation to a more distant school). Even when structures are in place, the ability to attend a different school is a stretch for some.