Three students lost their university places after a north-west London school gave them the wrong information about their A-level course.
Students at Copland Community School were told the AQA business studies course equated to two A-levels.
Two years later, on results day, they learned it was only worth one A-level.
Head teacher Dr Richard Marshall said: "This should never have happened." He said the school had now found university places for all three.
'Very bad reputation'
Harrison Mathias, who lost a place at the University of Bedfordshire to study business, said all the universities he had initially approached had turned him down.
He said: "I'm so stressed I just don't know what to do and I don't want this to happen to anyone else."
He said he was concerned none of the teachers seemed to be aware of the error.
"I did work hard and I had good grades, and we all did so much for this school because it had a very bad reputation."
Copland Community School was recently judged by Ofsted as inadequate and requiring special measures.
It was also banned from appointing newly-qualified teachers.
In the 2013 report, Ofsted said: "The sixth form is inadequate. Too many students do not achieve what they should in their AS-level examinations and do not carry on to A-level."
Dr Marshall, who was appointed head teacher following the inspection, said: "I have apologised unreservedly to these pupils and their families - this should never have happened.
"We have managed to help all three pupils find university places.
"I have assured the pupils and their families that I will not let this matter rest. I am investigating how this happened and will take appropriate action."
Harrison said he heard late on Monday that he had been offered a place to study business at GSM London, which reviewed his grades and predicament.
He said: "It's really good and I'm really pleased, it's very nice of them to take me on my grades."
But he added it had been a very stressful situation.
Brent Council added: "We sympathise with the pupils affected by this serious error.
"An investigation will take place at the school to identify where responsibility lies and appropriate action will be taken.
"We are working closely with the new head to address failings in the school."