Figures obtained by The Herald show nearly half of the 15 schools with the most pupils receiving support in their Highers in 2013 were in the private sector.
Leafy suburb schools in affluent areas such as East Renfrewshire were also well represented in the table. St Ninian's High School, in Giffnock, the best performing state secondary in Scotland, had 34 candidates receiving help last year, according to the Scottish Qualifications Authority (SQA) figures, compared to an average of seven for the rest of the country.
The highest figure was the 81 candidates who received exam help at the George Watson's College, in Edinburgh, with fees of more than £10,000 a year.
Overall, assessment arrangements were requested for 2570 candidates with dyslexia for all Higher subjects for the 2013 exam diet. That means 16% of all additional help is concentrated in just 4% of Scotland's 364 secondary schools.
The findings will fuel accusations from some quarters that dyslexia is a "middle class syndrome" with parents and schools pushing for extra help to maximise their exam results.
Some academics have even suggested there is no scientific proof dyslexics have problems any different from those encountered by others with reading difficulties.
However, other researchers argue dyslexia is a complex neurological condition whose sufferers require dedicated support to develop the reading, writing and comprehension skills essential to succeeding in school.
As a result, the SQA provides significant extra help for those diagnosed with dyslexia, which can include extra time to complete the exam, the use of a scribe to write down answers or allowing candidates to take electronic exams with the help of a spell-checker.
Scottish Parent Teacher Council said the figures made it clear a level playing field did not exist for young people in Scotland with dyslexia.
The council's chief executive, Eileen Prior, said: "These data make it clear that some schools are also more adept at leveraging the maximum support for these youngsters at exam time. Parents would be justified in asking why that is."
Cathy Magee, chief executive of Dyslexia Scotland, said the figures chimed with studies done by the charity which showed, for example, that a pupil with dyslexia in East Renfrewshire was five times more likely to get SQA assessment help than one in North Lanarkshire.
The Educational Institute of Scotland teaching union also said all pupils who require additional support should receive it, no matter the part of the country they live in. "It is essential all pupils are treated fairly," said a spokesman.
Iain Ellis, chairman of the National Parent Forum, called for effective screening for pupils at all schools.
Meanwhile, John Edward, director of the Scottish Council of Independent Schools, said it was no surprise private schools featured heavily in the table.
He said: "Schools in the private sector are increasingly identified by parents as hugely supportive of children with these types of conditions. Private schools have a focus on the needs of the individual child and are able to ensure they are supported in the ways they should be."