Private prison manager Serco is pledging to improve its performance after failing to meet 40% of its targets during its first nine months running Auckland's Mt Eden jail.
Since August, New Zealand's only private prison operator recorded three wrongful detentions and three wrongful releases at the prison, when it had a target of zero on both measures.
There have also been 10 serious assaults, almost double the rate allowed in its contract, and the company scored just 28% for its handling of prisoner management plans.
The company says it needs to do better, and it will be hitting 90% of its targets by the end of the year.
Serco managing director Paul Mahoney says the company will improve and is continuing to learn.
Mr Mahoney says Serco has so far paid about $200,000 in fines.
Corrections Minister Anne Tolley says the department is working closely with Serco to get it right.
The Howard League for Penal Reform says Serco is a multinational organisation which should have met its targets and the company's performance isn't good enough.