More than 150 international students gained fraudulent qualifications in less than a year from a failed school in Auckland.

Almost half were "ghost" students, who paid for qualifications but never attended classes.

An investigation into API Institute of Education, which closed in February last year, found at least 71 students were awarded a Diploma of Business but had no record of completed papers and did not appear on any class or marking lists.

The NZ Qualifications Authority report, obtained by the Weekend Herald under the Official Information Act, says a further 81 students attended classes but their marks were falsely reported to change fail grades into passes.

The academic records of many other students had gone missing.

The report was written by former API business programme leader Sarah Cozens, one of the staff members who blew the whistle on the scam. She now works for NZQA.

Her report says academic staff at the school were honest but were the victims of "administrative duplicity and managerial indifference" which NZQA should have spotted earlier.

"Frequently the results reported should have aroused suspicion among NZQA staff members."

The report said some students were "passing" up to six papers a semester, instead of the normal three.

"The paper choices were often random and illogical, with students passing Level 6 papers before doing Level 5 core papers, or doing pre-requisite and advanced papers in the same semester."

The report said some students had completely false results, suggesting a "package deal" presumably brokered by the education agents who refer students to schools for commissions.

Doctored results for individual papers could have been arranged by students or agents, possibly after a student failed a paper. There was anecdotal evidence that students could pay for higher marks in early 2009.

The report named nine agencies involved with the students but their names were blacked out in the copy released by NZQA.

Chief executive Karen Poutasi said the information was deleted to protect the free and frank expression of opinion by staff members.

She said as a result of the API investigation NZQA reviewed all providers of the Diploma of Business. Most needed to make only minor changes but the monitoring was still in place.

"Furthermore NZQA has intensively reviewed PTEs (private training establishments) in general where we have reason to believe there may be non-compliant behaviour."

Former staff and students have complained to the Weekend Herald that several other schools for international students have awarded diplomas to students who cannot pass their courses and in some cases can barely speak English.