The chairman of governors at an academy in Northamptonshire has said all state schools should be more independent.
Richard Tice, from Northampton Academy, said pupils had benefited since its conversion from a school in 2000.
He said GCSE passes had doubled over three years, truancy was down a third and teacher absenteeism had fallen.
Mr Tice's report is the first from within the academies system and has been submitted to think-tank Reform, which helps shape education policy.
Mr Tice said: "It has increasingly become clear to me that the freedom of the independent management structure devised for academies is the main driver to their success, where so many others have failed to manage these schools beforehand.
"Whilst the new facilities and buildings are an important, much-needed addition in a deprived inner urban area, they do not on their own improve overall performance.
"Far too much time in a pupil's career is spent preparing for government ordered exams and assessments, with the knock-on effect that their creativity - and enjoyment of subjects - is stifled.
"Fewer changes, testing, fixed coursework and exams would free up more teacher time for pupils' individual learning targets."
Mr Tice also criticised teaching unions, labelling them as a "blocker of reform" and urged them to become a "positive driver of change".
Elizabeth Truss, Reform's deputy director, said: "Academies still do not function as fully independent schools within the state sector and current plans will restrict their number to 13% of secondary schools."