Two-thirds of local education authorities failed to publish on their websites information about the additional support pupils with special needs should receive, despite a legal requirement to do so.
The survey of 12 LEAs inspected last summer, carried out by the Advisory Centre for Education, also found that the Office for Standards in Education is not monitoring whether councils meet their legal duty.
In some cases it has praised councils for communication with parents even when their websites fell short of legal requirements.
The latest figures follow a survey of all 150 LEAs in England last year which discovered that only 10 were meeting all the requirements introduced in 2001.
This year's survey found that Bristol's website still describes five stages of help for pupils with special needs. But the five-stage model was abolished by the revised code of practice more than two years ago.
A spokeswoman for the advisory centre, which offers independent help for parents, said: "The most serious gap is the continued lack of detail of what schools should be providing for children at School Action and School Action Plus - the levels of help which are expected to be made for children without statements.
"This is particularly worrying given the Government's emphasis on reducing the number of children relying on statements of SEN for any extra help," she said.
The centre will write to Ofsted asking it to check whether authority websites comply with the law.
An Ofsted spokeswoman said: "Ofsted will be responding directly to ACE. But we would like to make it clear that LEA inspections are conducted through a more comprehensive evidence base than access to LEA websites.
"This includes documentation from LEAs for parents, as well as inspecting the support provided through their work with parent partnerships to support parents of children with SEN."