A recent study in the Journal of Experimental Psychology shows that especially with kids who already have low self-esteem, it is not how much you praise, but how you praise that matters:
http://www.apa.org/pubs/journals/releases/xge-ofp-brummelman.pdf
http://www.wired.com/geekdad/2013/03/kids-with-low-self-esteem-the-parental-praise-paradox/
