There was research in "How We Decide" by Jonah lehrer that in a string of 3 tests, control group students who were told they succeeded on the first test because

There was research in "How We Decide" by Jonah lehrer that in a string of 3 tests, control group students who were told they succeeded on the first test because they worked hard did far better on the last test than students who were told they did well because they were smart.