A comparison of England's 15 city technology colleges with comprehensives with equivalent intakes found that the CTCs often achieved more than double the number of GCSE A*-C grades.
And the average improvement in the number of pupils at CTCs gaining five or more A*-C GCSEs since 1988 has been three times the national average at 12.33 per cent.
The Tories used the findings to back their call for all schools to be allowed to become city academies, the Labour equivalent of CTCs. Set up by the Conservative government in 1988, CTCs are independent schools funded by central government and privately-raised money.
Shadow education secretary Damian Green said: "City technology colleges show what can be achieved when heads and governors are freed from central control and given real power over the running of their schools.
"We welcome the creation of 20 more city academies by 2005, but this is just a drop in the ocean compared to the 3,500 secondary schools in England.
"Giving schools greater powers improves results - now we must give all schools this option."
Peter Simpson, principal of Brooke Weston CTC in Corby, Northamptonshire, where 98 per cent of pupils achieved five top GCSEs last year, said: "The autonomy we have has allowed us to do some things we wouldn't otherwise have had the freedom to do, such as operating a five-term year.
"But it is a matter of adjusting the autonomy to the needs of the school. Many heads value the support of their LEA and would not want to go it alone."