Ninety-five percent of the pass marks an Auckland tertiary institute awarded in two business diplomas were wrong, a Qualifications Authority investigation has found.
The authority has revoked International College of New Zealand's accreditation to offer three courses after 95 percent of the Level 5 and 6, and 70 percent of the Level 7 assessments were marked as a pass, when they should have failed.
The college had significantly failed to deliver the expected quality of education, the authority's deputy chief executive quality assurance, Grant Klinkum said.
"NZQA has monitored these business programmes and found that most of the assessments were marked by ICNZ as a 'pass' when they should have failed," Dr Klinkum said.
"As a result, we have withdrawn the credits ICNZ had awarded to students meaning they cannot be used towards a qualification. In most cases students will need to start their programme again with a new provider."
Dr Klinkum said the decision affected about 100 foreign students, who would be refunded their course fees.
The authority is warning other education providers that they should test the English of any former ICNZ students before enrolling them.
The authority blocked enrolments in the business courses earlier this year.
ICNZ was listed on the authority's website as a category 1 provider, its highest quality category, based on an audit conducted in 2013.
The removal of accreditation from ICNZ is the latest in a string of NZQA actions against providers.
In May, New Zealand National College halted four business courses after NZQA found evidence of plagiarism and poor marking and earlier that month, the authority cancelled the registration of Linguis International Institute because of serious concerns.
In January, the authority deregistered Aotearoa Tertiary Institute and late last year another Auckland institution, IANZ, was sold after the Qualifications Authority warned it was at risk of deregistration.