Dweck and Mueller* found that children who were praised for their "smartness" did roughly 25% worse on the final set of problems compared to the first. They were more likely to blame their poor performance on the difficult problems to a lack of ability, and consequently they enjoyed working on the problems less and gave up on them sooner.
Children praised for the effort, on the other hand, performed roughly 25% better on the final set of problems compared to the first. They blamed their difficulty on not having tried hard enough, persisted longer on the final set of problems, and enjoyed the experience more.
* Mueller, Claudia M.; Dweck, Carol S. (1998). Praise for intelligence can undermine children's motivation and performance. 10.1037/0022-35220.127.116.11