Psychologist Nigel Latta is warning that lobby groups which take up the cause of parents prosecuted for smacking their children are often misled.
Mr Latta is a member of the panel that has just completed a review of the child discipline law.
He says even where it appears there has been a massive overreaction, on closer inspection, all of the investigations he saw were justified.
He says part of the problem is that confidential information, for example past convictions, is not available to the public.
Mr Latta says that also leads to groups such as Family First not having the full story of parents whose cause they champion.
ACT MP John Boscawen says neither he nor Family First would deliberately mislead the public.
Radio New Zealand's parliamentary chief reporter says the review follows one released in November which found the new law had not led to parents being prosecuted for minor slaps.
Prime Minister John Key says the outcome of the latest review reinforces his view that the law is working.
The panel's recommendations include the establishment of a new parent support helpline within Child Youth and Family for parents who have questions about how they are being treated.
It also recommends that police and social workers be required to provide families with specific information about their rights and what to expect when they have to deal with the authorities.