Spanking Lowers A Child’s IQ, Researcher Says

Researchers from the University of New Hampshire found that children who are spanked have lower IQ’s than those who are not spanked.  More frequent spanking was linked to slower development of mental ability, but even infrequent spanking made a difference.  

L.A. Times
http://latimesblogs.latimes.com/booster_shots/2009/09/spanking-iq.html