The freedom of academies to write their own rules on admissions, exclusion, the curriculum and faith is laid bare today in a wide-ranging TES analysis.
A study of funding agreements signed between government ministers and sponsors of the first 27 academies reveals the extent to which schools are exercising their powers to deviate from the rest of the state sector.
Admissions policies alone expose huge diversity in the programme, which is being seen as the blueprint for Tony Blair's planned wave of independent trust schools, with extensive use of entrance tests, random selection and selection by ability.
Criticisms have been levelled at foundation and voluntary-aided faith schools, which also control their own admissions, with claims that their powers can be used to select pupils.
However, academy heads this week defended their admissions rules, saying they guarantee a wider social mix than most other schools.
The TES analysis shows that 12 academies select, or intend to select, some pupils every year by aptitude in a specialist subject. Another says this policy is under review.
Academies, like specialist schools, can choose up to a tenth of pupils by ability in subjects such as modern languages, music, performing arts, visual arts, sports, design and technology, or information and communications technology.
The proportion of academies employing aptitude tests - almost half - is much higher than the estimated 6 per cent of other specialist schools doing so.
However, funding agreements, which can be altered after they are signed subject to agreement by ministers, also reveal the extensive use of lotteries and banding systems, ensuring selection is not skewed towards gifted or middle-class pupils. At least four academies to date use random allocation to address over-subscription.
Two academies sponsored by the Haberdashers' Livery Company - Hatcham college and Knights academy, both in Lewisham - operate a system whereby at least 50 per cent of pupils are chosen at random.
Hatcham, one of the most successful state schools in London, received almost 2,500 applicants for some 200 places this year. Most comprehensives allocate their places on the basis of distance from the school gate, a system that has been criticised by Labour as "selection by house price".
The use of lotteries by academies indicates the Government's intention to encourage schools to thwart wealthier families who buy homes in the catchment areas of the country's best state schools.
Macmillan, in Middlesbrough, another successful city technology college, which adopted academy status last September, also chooses around half of children who apply from its "outer-catchment area" by the same means.
Banded entry tests are also widely employed by academies to ensure they achieve a greater mix. The TES analysis shows that nine academies use a banding system, in which pupils are required to sit a test (normally a written exam) and placed into four or five ability groups. An equal number is then chosen from each set, ensuring a comprehensive spread of abilities.
Peter Crook, principal of Peckham academy, said he believed every secondary should base their admissions on "fair banding" - a system the Government wants its new trust schools to adopt.
"Using the system means that we are knowingly turning down a percentage of brighter children who would definitely want to come to us," he said. "The result is that we are taking on more disadvantaged children than we would otherwise."
The use of tie-breaking criteria to admit pupils is typically varied and almost none of the 27 academies opened so far use exactly the same method to whittle pupils down, particularly when judging distance between home and school.
Stockley academy, in London, for example, say that the distance "from home to school is measured along the shortest walking route by public highway and lighted footpath". King's academy, Middlesbrough, meanwhile, prioritises children "whose front door is closer to the academy boundary as the crow flies than the nearest alternative school".
Academies also differ in the way they give priority to children with special educational needs, children in care and those with other social or medical requirements, including a physical disability that prevents them reaching another school.
The schools have attracted criticism in the past because their "independent" status gives them the power not to accept a child with a statement of special needs - a right not extended to other secondaries. Now a government-appointed arbitration panel has the final say when parents and academies disagree over a pupil's suitability for a place.