Corporal punishment as discipline is not only ineffective, it's damaging.

[morningfog]

81. Children Who Are Spanked Have Lower IQs, New Research Finds

Children who are spanked have lower IQs worldwide, including in the United States, according to new groundbreaking research by University of New Hampshire professor Murray Straus. The research results will be presented Friday, Sept. 25, 2009, at the 14th International Conference on Violence, Abuse and Trauma, in San Diego, Calif.

"All parents want smart children. This research shows that avoiding spanking and correcting misbehavior in other ways can help that happen," Straus says. "The results of this research have major implications for the well being of children across the globe."

"It is time for psychologists to recognize the need to help parents end the use of corporal punishment and incorporate that objective into their teaching and clinical practice. It also is time for the United States to begin making the advantages of not spanking a public health and child welfare focus, and eventually enact federal no-spanking legislation," he says.

http://www.sciencedaily.com/releases/2009/09/090924231749.htm

I know it's too late for you, but perhaps you can help your grandchildren. I hope this helps to educate you.