Expanding Crawley's six secondary schools would not be enough to meet the demand for places, West Sussex County Council has said.
The comment came after the Department for Education announced a new free secondary school for Crawley.
The application for the provisionally named Forge Wood High School was one of 131 approved by the Department for Education in an attempt to create thousands of places countrywide.
The new school will be run by GLF Schools, which has already opened Forge Wood Primary.
Henry Smith MP took to social media to welcome the free schools, but Michael Ferry, of St Wilfrid's School, in Southgate, said he and other headteachers had repeatedly told the council Crawley did not need another secondary school but should expand the ones it already had.
Mr Ferry said meetings had been held with the council for years, exploring the option of expanding the town’s secondary schools by one or two classes per year group.
Accusing the council of wanting to provide education “on the cheap”, he added: “As a group of headteachers and senior leaders, we have been consistently fobbed off. Whether it be funding or places. When will people in positions to make decisions on education listen to those who know what they’re talking about?
“Then, to see Henry Smith’s tweet about how he welcomes this news, just reinforces to me that the people running education are clueless, they really don’t understand schools and how they work. They believe in a market economy that simply doesn’t work in education.
“Crawley doesn’t need a new school, it needs the powers that be to work with people who know what they’re doing and trust them – heads and senior leaders of Crawley schools.”
A council spokesman said: "In West Sussex we welcome the mixed economy of schools that is developing and aim to work in partnership with all our education providers to offer parents a choice.
"The announcement last week of the latest approved free schools in West Sussex included a new secondary school in Crawley. The planned opening of this school will help alleviate the increase in secondary pupil numbers which is likely to be experienced in Crawley over the coming years as a result of the current increase in demand for primary places together with the additional new homes in the area.
“We have been working with headteachers of existing secondary schools in Crawley on expanding their schools.
"However our longer term place planning information shows that although there is some spare capacity in existing buildings to expand these, demand is likely to be so high that expanding existing schools will be insufficient in the longer term.”
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