The Long-Term Effects of Spanking

This article describes a recent research study from Tulane University that links spanking to more aggressive behavior in children.  Almost 2,500 children participated in the study, which found that children who had been spanked twice or more in the month prior to participating in the survey at the age of 3 were 50% more likely to show aggressive behavior at the age of 5 than other kids.  

Time Magazine
http://www.time.com/time/magazine/article/0,9171,1983895,00.html