Carol Dweck's assistants praised the children after they did well on a test.

Dweck sent four female research assistants into New York fifth-grade classrooms. The researchers would take a single child out of the classroom for a nonverbal IQ test consisting of a series of puzzles—puzzles easy enough that all the children would do fairly well. Once the child finished the test, the researchers told each student his score, then gave him a single line of praise. Randomly divided into groups, some were praised for their intelligence. They were told, “You must be smart at this.” Other students were praised for their effort: “You must have worked really hard.”

So, it was not efforts or intelligence per se they were praised for. They were praised for having a reason to be good in that series of puzzles (of course, in this particular case, children were told what the "reason" was). Of course, it would probably be interesting to test whether praising children for results and results only, without any allusions to what might have been a reason for their success (leaving that to children themselves to deduce), is good or not.