The Association of School and College Leaders (ASCL) have warned that proposed changes to give schools control over term times may turn into a "free for all".
The ASCL said schools currently follow the local authority calendar because it suits parents who have children in different schools.
The problem will come if no one is responsible for creating a coordinated calendar for an area and it turns into a free for all. Somebody needs to take the lead locally on deciding term dates and it makes sense for this to be the local authority, even if schools aren't required by law to follow it.
It would help for deregulation to be accompanied by guidance which reminds schools to take into account local circumstances and to consider the practical difficulties parents can face when schools within an area have varying term dates.
More top news
A British couple with a combined age of 194 are to become the world's oldest newlyweds when they marry in the summer.
Weekend weather starts wet for some
Manchester United manager Louis van Gaal says Ryan Giggs will almost certainly succeed him at Old Trafford.