Child, Youth and Family says its staff are not leaving in droves despite a high workload.
The welfare agency says notifications have quadrupled in the past eight years to over 150,000 per year and it has taken on 250 more social workers to cope.
After complaints from frontline staff, Child Youth and Family will conduct a review of case numbers for social workers. It says an ideal average is between eight and 18, depending on their complexity and the person's experience.
CYF deputy chief executive Bernadine MacKenzie says 80% of her staff have more than two years' experience, with an average of seven- and-a-half years.
"I'm really proud of my staff and what they do, they do an exceptional job. It's never easy to get experienced workers and to get the right people in this job - it's a tough job. So obviously recruitment is pretty crucial to us."
Ms MacKenzie says the agency's staff turnover rate has also dropped in five years from 16% to 11%.
But professional body the Association of Social Workers says its members at Child, Youth and Family are having to deal with huge caseloads and accounts from the agency are that numbers range from 27 to 44.
The association says its members are hesitant to raise problems caused by their heavy workloads with management at Child, Youth and Family for fear they will be put on notice.
Chief executive Lucy Sandford-Reed told Radio New Zealand's Morning Report programme that at times staff are being put on performance improvement plans when their caseloads drop to about 18.