Praise is important but it has to be well-founded and sincere. Students quickly pick up on empty praise which may have the completely opposite effect of what was actually intended.
A study at Columbia University (Claudia Mueller and Carol Deck, 1998) came to the conclusion that praise for effort was more beneficial than praise for intelligence. In fact, young learners who were praised for their intelligence (“You’re really clever!”) rather than the effort they put into a task (“I can see you worked very hard on getting this result. Well done.”) were less likely to persist with tasks after an experience of failure.
Research suggests that intelligence is perceived as a fixed trait by children while effort as something that is within their control and therefore can be improved upon.