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
Here are just some of the faces and stories of Auschwitz survivors 70 years on from the concentration camp's liberation.
Labour is promising to increase nurse training places if they win the General Election, to cut costs and boost supply.
The final of the 'Big 6' energy firms to cut prices - EDF - has announced it is reducing gas tariffs by just 1.3%.