Many dyslexic youngsters are lagging behind their peers because teachers will not have them statemented until their reading ability is at least four years below their chronological age, according to the British Dyslexia Association.
The association says this delay "represents a catastrophic educational failure for the dyslexic child".
A survey of 102 local authorities found that dyslexic 10 or 11-year-olds generally did not get statements until their reading age dropped to that of a six-year-old, or lower.
It found that parents were being told that their children could not have specialised help without a statement but, at the same time, that their literacy levels were not poor enough yet for a statement.
The BDA study found that this policy was leading to a "widespread and unacceptable tolerance of underachievement" in schools.
"This means that many children still have unproductive and unhappy school careers. This waste stays with them all their lives," the study says.
"Dyslexic children will not develop as whole persons or become effective members of their community unless their difficulties are properly identified and appropriate support given."
The BDA has called for the Code of Practice for identifying and assessing special educational needs to be implemented "systematically" across the country.
It found that a third of local authorities had set general policies for special needs but had not defined specific areas such as dyslexia. Another third of those responding said they could not produce their criteria for statementing.
One of the most common complaints by parents to the BDA's telephone helpline was that schools were reluctant to identify children as dyslexic, often because the local authority did not recognise the condition. This led to a lack of support and aggravation of the child's educational problems.