The City Academy programme came under renewed pressure this week after it emerged that each costs £8m more to build than a conventional school.
The figures were released in a report by think tank New Philanthropy Capital, which questions whether the academies represent the best use of the money donated by private sponsors.
Figures compiled for the education select committee show that the cost of an academy place is about £21,000 a pupil, compared with £14,000 for a normal school. This adds up to a figure of £17m for a conventional school and £25m for an academy. The report says: "The £8m discrepancy could pay the wages of 276 teachers for a year."
The news comes as cost overruns have been reported on two key academy projects.