So, did you ever need to leave extreme marks on their butt, arms and legs?
I personally found that one whack square on the rearus endus was enough. I actually went more for the big sound than the big hit (cupping your hand will do that). By the time the kids were 13, though, this was not necessary at all.
Obviously, not being there, I can only imagine, but the kind of marks left here (if the story is accurate) reflect that the parent was hitting not to discipline, but as a means of acting out his own issues.
IMHO, if you are still resorting to spanking when your child is in the 8th grade, you might want to reassess the approach you are taking with the kids. Again, for you serial spankers at age 13 and beyond, this is JMO.
Bingo!