The Court of Appeal has reserved its decision on an appeal by the first person convicted under the child discipline law.
Christchurch musician James Mason was convicted last year of assaulting his son by punching him in the face in 2007.
Mason was convicted of punching his then four year old son in the face and pulling his ear after he saw him and his two year old brother riding their bikes dangerously.
He was sentenced to nine months' supervision and to attend anger management classes.
Mason represented himself in court on Tuesday, supported by his wife.
Despite eye witness accounts, Mason has always maintained that all he did was flick his son's ear and pulled his long hair and wants his conviction for the more serious offence quashed.
He told the Wellington court that if he had punched his son in the face, his son would have been injured, which he wasn't.
He says that, initially, police accepted his explanation, issuing only a warning.
