Most kids never need a smacking, I have six kids who between them were only smacked 4 or 5 times at the most. That’s an average of less than once each but, in reality, my eldest was the main recipient! Was it that we were harder on him? Probably! There are many reasons why the first child is more firmly disciplined than the rest. The parent’s inexperience is the main thing; their expectations are greater when they’ve never been through bad behavior before.
Two other reasons A) The eldest usually feels he has to show off in front of his younger brothers and sisters. B) when a younger one sees their elder sibling being chastised it has more effect on them than it does the child being smacked. That’s the main reason why I think school CP is an effective punishment – its effect on the onlookers!