I've just seen this rather fascinating video, originally posted on the irvingparentsforum. I picked it up on the kitchen table math blog, posted by the inimitable Catherine Johnson, and it's certainly worth sharing.
The context for the interest in this subject relates back to a story, reported by npr, that broke into the news earlier this week in the USA about bonuses for teachers and whether they are effective in raising standards.
So, does paying out big bonuses work? According to a study by Vanderbilt University's National Center on Performance Incentives, which looked into whether paying teachers big bonuses for improving pupils' tests scores works and 'was described by the researchers as the nation's first scientifically rigorous look at merit pay for teachers', it doesn’t!
The youtube video may explain why. Watch and enjoy!