One in four parents faced opposition when choosing a mainstream school for their child over a special one, the survey commissioned by the Down's Syndrome Association found.
The survey also uncovered variations in support for the children, with 23 per cent of younger primary pupils not receiving speech therapy - even though around half of Down's syndrome children have a specific language difficulty.
There were also differences in the number of learning support assistants and in their qualifications and training.
The situation seems to be improving, however, as parents of younger children entering the system have fewer complaints than those of older pupils.
Having gained a mainstream primary place, 84 per cent of the parents surveyed were content with the way the child's needs were addressed.
"We are aware that a number of local education authorities are unwilling to provide the support required to allow children with Down's syndrome to attend the school of their choice which, for many parents, is the local mainstream school," said Carol Boys, the association's director.
"We appeal to authorities to abide by the spirit of the law laid down by the Education Act and to make suitable provision."
The issue was highlighted in a recent Channel 4 documentary, featuring Northern Ireland teenager David McKibben.
He wanted to stay with his primary classmates when they moved to the local secondary school, but was refused a place and is currently receiving no education at all, the association said.
The survey, covering the academic year 1997-98, drew responses from 319 parents in 107 education authorities. Nearly one quarter of parents said they would like more focused training for staff.
The survey report "Experiences of Inclusion" is available from Kate Thomas or Sarah Waights at the Down's Syndrome Association, telephone 0181 682 4001