The Independent Children's Home Association (ICHA) has called for the Department for Education to intervene and do more to support admissions after 58 per cent of children's home providers who responded to a survey said they do not think the Schools Admissions Code for Looked-After Children is being honoured by mainstream schools.
The code specifies that looked-after children should be given the highest priority in school admissions, even where there is oversubscription for places, according to the ICHA, which commissioned the poll of 53 members.
The average period before a mainstream place is secured is 3.1 months, with 54 per cent of providers reporting one or more instances where children have waited for up to three months - around a term and a half - for a mainstream school placement.
Some 43 per cent reported waiting more than three months and 24 per cent of respondents report they have lost a lot of referrals due to the inability to source a mainstream education place for the referred child.
A similar level reported local authorities moving children on after the child had already been placed in the home, because of the lack of a school place.
Jonathan Stanley, chief executive of the ICHA, said the research shows how "looked-after children in children's homes are discriminated against by many schools".
"The research provides evidence that some of these children are refused admission solely because they currently live in children's homes," he added.
"The admissions code for looked-after children allows for the Secretary of State to direct schools to take children. This power has been used exceedingly sparingly, to the detriment of looked-after children in children's homes.
"The Secretary of State must act to ensure the legal entitlement to looked-after children is delivered."
The Department for Education said: "We are committed to ensuring that children who are in care or who have been in care are supported to succeed in education and are admitted to school without delay.
"The School Admissions Code requires all school admission authorities, including academies, to give the highest priority in their admissions criteria to looked-after and previously looked-after children.
"If a school refuses to admit a looked after child, they can be directed to do so by either the local authority if it is a maintained school or the Secretary of State if it's an academy.
"Children in care also benefit from the support of virtual school heads and designated teachers, and the Pupil Premium Plus - worth £2,300 per child."