I read an interesting paper once, I think it was The Science of Spanking or something close. It covered the correlation between spanking and aggressive/defiant children. One perspective was that children who were spanked, grew to be more aggressive/defiant than children who weren't spanked. An alternative view was that children who were spanked, were likely more aggressive/defiant to begin with. In my experience, I find the second hypothesis to be more likely. I didn't answer the poll, though because I feel the choices were too narrow. I believe that it depends on the child.