Multi-million pound expansion at Westhoughton High School has been approved but councillors warn it will not meet future demands.
A new two-storey classroom block will accommodate an additional 200 pupils over the next four years.
But councillors said new developments in Westhoughton mean more places will need to be created to cope in the future.
The planning committee approved proposals to demolish an existing block and build a bigger one at a meeting.
Labour councillor Anna-Marie Watters, who represents Westhoughton South, welcomed the plans but warned that developers have put the town in a “desperate situation”.
She said: “This committee is well aware of Westhoughton being of under threat by greedy developers who are determined to rip up our green belt. The extra spaces created by this extension will only meet our current need for desperately needed school places.
“We do need to be very clear, that Westhoughton does not have enough school places to accommodate the children within Westhoughton.”
Her fellow ward councillor David Wilkinson agreed, saying a new school will need to be built to cope with demand.
Westhoughton North and Chew Moor Conservative councillor Zoe Kirk-Robinson moved to approve the application saying: “We badly need the school places”.
The planning committee voted unanimously to approve the application. A total of £2.4 million will be spent on expanding the school but because of demand for school places, Westhoughton High School has already begun to admit higher pupil numbers.
Starting from this academic year, each Year 7 intake will have an extra 40 children. This funding was approved by the executive cabinet member for children’s services, Cllr Ann Cunliffe, in August.