By Hannah Richardson
BBC education reporter at the ASCL conference in London
John Dunford is stepping down as ASCL general secretary after 12 years
Conservative education plans could lead to a "corner shop" system of 20,000 autonomous schools, the Association of School and College Leaders has warned.
The poorest would suffer the most under Tory plans to let parents set up "free schools" outside council control, said outgoing ASCL head Dr John Dunford.
He also warned against a "false belief" the market would improve standards.
The Tories say their schools would raise standards through smaller class sizes and more parental involvement.
In his final speech to his association's conference as general secretary, Dr Dunford said school and college leaders had learned to work well together for the good of all young people in their areas.
"We want to see the new government build on this collaborative culture.
"We do not want to return to bad old days of dog-eat-dog policies in the false belief that a good dose of the market will improve standards."
He added: "It will be the disadvantaged who suffer if the school system splits into 20,000 autonomous units - a corner-shop version of the education system and not one that this association supports."
Dr Dunford's comments were an attack on the Conservative policy of letting parents set up their own so-called free schools, independent of local authority control but funded directly by the state.
But Tory education spokesman Michael Gove told the conference there would be a greater degree of freedom and autonomy across the education system if his party won the election.
He also said that there would be extra cash for schools in disadvantaged areas through the party's pupil premium - whereby money is attached to pupils from poor backgrounds.
Mr Gove added: "It's about being allowed break free from political interference, not about applying the tourniquet even more tightly."
Dr Dunford also attacked government meddling in schools saying that, between September 2009 and last month, every week there had been an average of 2.5 pieces of a type of government legislation known as a statutory instrument affecting schools in England and Wales.
"The highest was eight in a single week. Only one week was there no statutory instrument. Michael Gove has promised to reduce this if the Conservatives win the election.
"If they do I shall hold them to it. We don't want Labour bureaucracy replaced by Tory red tape."
In September, Dr Dunford is stepping down as ASCL general secretary - a post he has held since 1998.
On Friday, Children's Secretary Ed Balls gave him a framed letter from Gordon Brown thanking him for his contribution to the education system and debate.