DUBBO College Delroy Campus is the state's second-most rundown school, education department data from June last year shows.
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The documents obtained under freedom of information and released by the NSW Opposition on Monday showed the campus had a $2.9 million maintenance backlog of works at the end of June 2015.
Its state of disrepair was second only to Great Lakes College Forster Campus, which is needing $3.4 million in works.
Dubbo College South Campus was 16th worst of country schools and ranked 66th worst in the state with its $1.1 million maintenance backlog.
Opposition leader Luke Foley said the mounting $732 million repair bill for the state's public schools could endanger students if the backlog was not addressed.
But the government hit back at the claims, saying Labor left behind a bigger backlog bill nearing $1 billion.
"We have school students in NSW sitting with leaky roofs, leaky gutters, busted toilets, broken windows."
- Opposition leader Luke Foley
Examples of work needed at Delroy Campus include to its sewerage system, floor coverings, ceilings, roofs and stormwater, according to Labor.
Maintenance work completed between July last year and February this year totalled a $128,692, a far cry from the $2,927,543 needed.
Labor says at the current rate it would take 15 years to complete Delroy's backlog.
Country NSW high schools filled seven of the top 20 most dilapidated schools.
Mr Foley said the maintenance backlog surged by $195 million - more than 36 per cent - under the Baird government and spending was being outstripped by the growing bill.
"It's a crisis," he said.
"We have school students in NSW sitting with leaky roofs, leaky gutters, busted toilets, broken windows."
But the government hit back at the claims, saying it had inherited a bigger backlog bill nearing $1 billion from Labor.
"Since 2011, the government has committed almost $4 billion to school infrastructure and maintenance, with more than $342 million allocated in 2015-16 for school maintenance," acting education minister Leslie Williams said.
A Department of Education spokesman said since 2011, the NSW government had committed more than $30 million for capital works and maintenance in public schools in the Dubbo electorate.
At Delroy Campus recent work included drainage improvement, painting, carpet and vinyl replacement, toilet repairs, ceiling repairs, door replacement, window repairs, he said.
Future maintenance priorities would include a focus on the school's stormwater drainage system, he said.
At South Campus maintenance has recently been carried out on the Technical and Applied Studies (TAS) unit, he said.
Maintenance during the April 2016 school holidays included the provision of insulation to some rooms, he said.
