It happens naturally, no reason to force beforehand. The natural selection is also happening among the top caliber students who just do not have what it takes. The key is to adjust to the higher level of academic requirements at college in some majors / tracks. If this initial adjustment does not happen, then they fall off from their initial track.
Sir John Gurdon’s school report, quoted in #5, makes a good story, but it needs to be regarded as an outlier for several reasons. For one, he was a student at Eton. Marking and teachers’ comments there are unlike the grading and comments in the US. For a second, Gurdon was admitted to Christ Church, Oxford, initially to study Classics, but he changed to Zoology. Even among Oxford Colleges, Christ Church is rather exclusive.
@PrimeMeridian, in that analogy, each date would cost 5-6 figures.
Under those circumstances, I think people should be a bit more careful of whom they date.