Most current research:
Spanking Kids Increases Risk of Sexual Problems
http://www.unh.edu/news/cj_nr/2008/feb/lw28spanking.cfm
Use of Spanking for 3-Year-Old Children and Associated Intimate Partner Aggression or Violence
http://pediatrics.aappublications.org/cgi/content/abstract/126/3/415
Spanking Can Make Children More Aggressive Later
http://tulane.edu/news/releases/pr_03122010.cfm
Spanking Children Can Lower IQ
http://www.unh.edu/news/cj_nr/2009/sept/lw25straus.cfm
Just a handful of those helping to raise awareness of why child "spanking" isn't a good idea:
American Academy of Pediatrics,
American Academy of Child and Adolescent Psychiatry,
American Psychological Association,
Center For Effective Discipline,
Churches' Network For Non-Violence,
United Methodist Church
Nobel Peace Prize recipient Archbishop Desmond Tutu,
Parenting In Jesus' Footsteps,
Global Initiative To End All Corporal Punishment of Children,
United Nations Committee on the Rights of the Child.
In 31 nations, child corporal punishment is prohibited by law (with more in process). In fact, the US was the only UN member that did not ratify the Convention on the Rights of the Child. The US also has the highest incarceration rate in the world.
The US states with the highest crime rates, poorest academic performance, and highest obesity rates and health problems, are also the ones with the highest rates of child corporal punishment.
There is simply no evidence to suggest that child bottom-battering instills virtue.