Many academies are not making changes to their school day or term times, despite being given the powers to do so, a report suggests.
More than half of academies have not decided to alter their school year while three-quarters have decided against changing the length of the school day, according to a study by the Schools Network and the think tank Reform.
It reveals that concerns about inconveniencing parents, fears over union activism and reliance on council-run school transport is stopping many academies from taking up these freedoms awarded to them by government.
The study also shows that the main reason for schools to become an academy is the prospect of extra money, as well
as the general sense of control over their budgets.
Academies are semi-independent state schools which receive their funding directly and have more control over areas including the curriculum and staff pay and conditions.
The schools were originally set up under Tony Blair's Labour government and were aimed at boosting standards in the poorest areas.
Education Secretary Michael Gove has now opened up the scheme to all state schools, with more than 1,600 converting so far.
The new report questioned 478 academies - almost a third of the total number - about how they are using their freedoms.
The findings show that 55.4% of academies have decided not to alter the school year, although one in five (20.6%) have done so and 15.3% are considering it.
The report says that many are making minor changes, such as slightly lengthening half terms or shortening summer holidays, while a "small number" are considering radical changes such as moving to a five-term year.