Two London local authorities have amended the sibling priority rule from 2016, taking away the automatic entitlement to school places for a number of families.
Brent and Wandsworth councils will stop giving priority to siblings if their family no longer lives within a catchment area.
In contrast, other councils have recognised the strain parents will be under if they have to take their children to at least two different schools.
Local authorities and schools that run their own admissions must consult on their arrangements every year by April 15, even if there are no proposed changes.
In Wandsworth, south London, families must remain living within 800 metres of a primary school to be entitled to automatic places for younger brothers or sisters.
The council said some families that had moved were getting places for their younger children ahead of applicants who lived nearer the chosen school.
A council spokesperson said: “This is all about making the system as fair as possible for parents who want their children to attend their local neighbourhood school.
“What we are saying to parents is that if you continue to live near your school of choice, your younger children will retain their sibling priority.
“But if people choose to move away from the area then children from these families will no longer have preference over children who live much closer to the school. It cannot be fair that a child who lives miles away gets priority over one who lives only yards away.
“We don’t, however, want to disadvantage parents who have acted in good faith, so this change will not come into effect until September 2016 and will not apply retrospectively, so the younger brothers and sisters of children already at a school will not be affected.”
Meanwhile, councillors in Brent, in the north of the capital, agreed to the same change. However, it only had two responses to its consultation – both from primary schools – one for the change and one against.
Council officers said families were less likely to be split up due to a “social/medical criterion”, which is aimed at children who need to be close to home for medical reasons, or if they have special educational needs.
Similar proposals were also put forward by Leeds City Council, but of the 1,917 consultation responses, only four supported the idea, and so it was not pursued by the authority.
In Ealing, west London, the council removed the rule that siblings living outside a school’s catchment are given less priority than those within it. It said this would make it less likely that parents would need to juggle taking their children to different schools.
Ealing also said that it would now consider applications on a “straight-line” basis, rather than a “catchment area”. This would remove the “anomaly” of families not being able to get into schools because of where the boundary falls.
Ealing councillor Binda Rai, cabinet member for children, said: “It is always difficult to make changes to a system that affects so many people, but, on balance, I believe these updates will make the admissions system fairer for local families.”