A college principal said he had days to start working on an extension for more than 200 extra students - or risk losing millions of pounds of government funding.
Tim Fisher, principal of the Queen Elizabeth Sixth Form College, spoke of their need for a new floor to an existing two-storey extension for two new classrooms, work areas and storage.
The school applied for planning application for the new level, meant to accommodate 233 more students expected to come to the school on Vane Terrace, Darlington.
It attracted objections from residents plagued with parking and congestion problems.
But Mr Fisher told councillors he had a "moral and educational imperative" to provide the best possible facilities and learning opportunities for his students.
He said: "My job is to make sure that for all those who are qualified to attend, we offer the opportunity for them to thrive, fulfil their ambitions and go on to live out their dreams. It's as straightforward as that."
The college had attracted over £2m in government funding for a capital project, Mr Fisher said at a Darlington Borough Council planning meeting.
"The danger for us is if we don't proceed with the project extremely quickly, we'll be in a situation where that money has to be returned to central government," he added.
"I think that would be a disastrous situation for those young people because it's my view that's their money, it's an investment in their futures.
"We don't want a significant amount of money that's been allocated to the young people of Darlington to go anywhere else.
"I want that resource to go to them because they deserve it."
Asked later how tight the timescale was on the £2m funding, he replied: "Very. If we don't begin work on this project, literally physical work, next week, we're in grave danger of having to send it back in large amounts.
"It really is imperative to us that this decision is made as quickly as possible so that we can proceed."
The school was previously refused permission for an extension for more than 400 students.
The plan attracted 16 objections, saying the extension would add to an "eyesore", was not in-keeping with the Victorian building and would worsen parking woes, traffic congestion, obstruction and danger on packed streets.
They also raised concerns about pollution, litter, anti-social behaviour, disruption and noise.
Ward councillor Matthew Snedker said he had been "inundated" with communications raising long-term concerns affecting people's day-to-day lives.
He said: "The long-term disturbance and serious inconvenience to residents have steadily increased and, to be fair, many of them have had enough.
"It's not against the college, it's not against the great work they do in the community.
"But this development seems to be oversized, will exacerbate the existing persistent problems that residents feel, and is part of a narrative of continued ever-expansion, and residents are asking 'when will we stop?'"
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Planning manager David Coates said the latest plan was for fewer students, had an improved travel plan and the college would contribute £25,000 towards a pedestrian crossing at a pinch point on Stanhope Road North.
He said the design was a "significant improvement" on the existing 1960s building and the scheme would have community benefits in supporting the college increasing its learning space and quality.
He added they were not considering closing the college as some objectors suggested.
Cllr Gerald Lee said: "It is so important that we give as much support as we possibly can to every student going through Darlington colleges."
The committee voted unanimously to approve the plan with conditions.
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