The Teachers' Disciplinary Tribunal has censured the former principal of Pamapuria School, Stephen Hovell, for failing to protect pupils from the paedophile teacher James Parker.
But it has stopped short of cancelling his registration as a teacher.
Mr Hovell was suspended, and later resigned, after Parker was arrested in Northland in 2012 on multiple charges of sexual offending against young boys.
The Teachers Council alleged that Mr Hovell was guilty of serious misconduct, on the basis that his management of the school was so deficient he did not prevent Parker from behaving as he did.
The tribunal said there was no evidence that Mr Hovell knew about Parker's offending, or could have stopped it, but his failure to stop Parker taking boys home after a warning letter from the police, was negligent and incompetent.
Parker was sentenced to preventive detention in August last year for 74 sex charges relating to sleepovers with boys at his Awanui farm between 1999 and 2012.
The police wrote to Mr Hovell in April 2009 saying it was inappropriate for the teacher to have young children sleep over.
Mr Hovell said he had a stern talk with Parker over the letter but there was nothing more he could have done.
The tribunal found Mr Hovell guilty of misconduct, saying if he had acted on the concerns at the time Parker's behaviour would have come to light a lot sooner.
Mr Hovell admitted the serious misconduct. He has not taught since 2012 and is unlikely to again, but he was allowed to keep his teacher's registration.
The tribunal said Mr Hovell had a long previously unblemished record in education, and it would not cancel his registration, on the understanding he would not teach again.