New figures show only two people have been prosecuted for smacking their child since child discipline legislation was passed in 2007.
In their sixth review of the law, police say they looked at 367 cases of child assault - 11 involved smacking and 39 involved what were called minor acts of physical discipline.
The 11 smacking cases led to one prosecution, which ended in the accused receiving diversion, and eight warnings.
Of the 39 minor acts of physical discipline, one resulted in prosecution, and 37 produced warnings.
As a result, there have been two prosecutions since the law was passed.
Police say this shows they are using discretion as planned when the law was passed. and say the guidelines are working well.