Po Bronson has an excellent article titled How not to talk to your kids: The inverse power of praise in the New York magazine. It's a must read for all parents. In fact, its 'lessons' could be used in all kinds of human interactions, including teaching. Here's a key take-home message:
... “When we praise children for their intelligence,” Carol Dweck wrote in her study summary, “we tell them that this is the name of the game: Look smart, don’t risk making mistakes.” And that’s what the fifth-graders had done: They’d chosen to look smart and avoid the risk of being embarrassed.