He figured that the way to distinguish nature from nurture was to give people the same amount of practice at a certain task and to see whether they became more or less alike. If their skill levels converged, Thorndike reasoned, then the impact of practice was overwhelming any innate individual differences. If they diverged, then nature was overpowering nurture.
In one experiment, Thorndike had adults practice multiplying three-digit numbers by three-digit numbers in their heads as quickly as they could. He was astounded by their improvement.
[...]
After one hundred practice trials, many of the subjects cut their mental computation time in half.
[...]
But while Thorndike saw across-the-board improvement, he also noted what sociologists often call a “Matthew effect.”
[...]
Thorndike saw that the subjects who did well at the start of the training also improved faster as the training progressed compared with the subjects who began more slowly.
Georgia Tech psychologist Phillip Ackerman has found that, in simple tasks, practice brings people closer together, but in complex ones, it often pulls them apart.