Are there any reputable studies on spanking?

Question

Is there any scientific evidence that non-harmful spanking does or does not exist? Furthermore, is it ever effective (whether or not it is harmful)?

Answer 1

Here is the resolution on corporal punishment by the American Psychological Association.

The resolution includes this part:

Research has shown that the effective use of punishment in eliminating undesirable behavior requires precision in timing, duration, intensity, and specificity, as well as considerable sophistication in controlling a variety of relevant environmental and cognitive factors, such that punishment administered in institutional settings, without attention to all these factors, is likely to instill hostility, rage, and a sense of powerlessness without reducing the undesirable behavior

This indicates that punishment can be used effectively. However, there are a number of variables that make it generally impractical, as mishandling these variables will most likely result in severe negative consequences, in addition to failing to adjust the behavior as intended.

Unfortunately I do not have direct access to the research that the association referenced to arrive at this resolution.

Answer 2

Here is the problem with most studies conducted on children. Todays mainstream view on spanking is if you spank a child you'll produce an aggressive individual.
And as evidence we're presented with violent people who where beat by their parents and they conclude the relationship.
None of those studies are controlled on genetics. Children are not blank slates, they do come with predetermined sets of personalities, which of course are not complicity fixed, but it would be foolish to ignore them.
For example child from a violent parent can be violent because of her/his genes, as many of other distinct physiological treats, for example temperament, curiosity, sense of humor etc.
There is another part to this story and of course it's the intensity of physical reaction towards the child, spanking and hitting the child with a fist should not be put in the same category as it's done in popular parenting manuals.

There are situations where spanking is absolutely the only way. If you have a child that continually does something which indangers her/his life, like poking fingers into electric socket, and you say "no", than "NO", than "NOO!", and she/he just laughs and continues to do so, you need to physically remove the child from harms way. Trying to explain the concept is good of course, but if it doesn't work you need to spank the child.
There is no proof that spanking is not the right method of parenting in combination of other pedagogical measures.

EDIT:
I've been asked to give you studies and to go through these studies to explain my claims. I will not do that because it would take enormous amounts of time to go through all the details, it's much easier just to post articles than it is to dissect them and explain every flaw and links to all the studies are not free.
However I will give you a paragraph from Harvard psychology professor Steven Pinker's book The Blank Slate about his opinion and youtube link where he explains it in nice 24minutes talk (I'll also post the minute where he talks about parenting), with slides from some studies of human brain and behavior.
Also I'd like to ask a question if any of you in any media have ever seen an explanation of pedagogical study where genes where included in explanation? Even if you have the frequency of such articles is vastly outnumbered by ad hoc explanations of cause and effect. Yet it is so obvious to anyone who has ever interacted with another human and his parents/brothers/sisters/twins.

The Blank Slate: The Modern Denial of Human Nature

Chapter 19: Children page 375
..."The First Law implies that any study that measures something in parents and something in their biological children and then draws conclusion about the effects of parenting is worthless, because the correlations may simply reflect their shared genes (aggressive parents may breed aggressive children, talkative parents talkative children). But these expensive studies continue to be done and continue to be translated into parenting advice as if the heritability of all traits were zero."

Here is a youtube link, it would be good to look at the whole video (24minutes) because you'll lack context if you watch only the part about parenting that starts at 18:28:

Steven Pinker:Chalking it up to the blank slate

What I wanted to offer from the start to person who asked the question is caution when s/he looks at studies and answers, because in psychology/pedagogy while there are a lot of brilliant scientists, lot of scientists from these fields don't understand the basic scientific principle and don't have scientific integrity. S/he needs to be very skeptical when s/he follows the advice given here or from the associations of psychologists.