The findings, which will be presented to a major international conference in Glasgow next week, have prompted calls for further examination of current practice on the inclusion of deaf children to ensure they are not being failed.
Details of the Achievement of Deaf Pupils in Scotland Project (ADPS) will be given to the Inclusive and Supportive Education Congress by Marian Grimes of Edinburgh University. The project was set up in 1998 following an investigation south of the border which found there had been no improvement in the achievements of deaf pupils since a landmark study in 1979 revealed that the average reading age of a deaf school-leaver was nine years.
Ms Grimes and the project team have amassed evidence that proves deaf children continue to underachieve significantly compared to their hearing peers. But she warned: "We are only touching the tip of the iceberg here.
We need to track groups of children and understand what factors are making a difference to their attainments over time."
The research included interviews with young people, as well as surveys and observational data, which show there are inconsistencies in expectations and in the range of strategies available.
One study of 14 British Sign Language (BSL) pupils in 2003 found a wide variation in the hours and qualifications interpreters provided. Another found the experiences of deaf children in school were disappointing. Many reported feelings of isolation and frustration, and said that they had to leave school before they could develop a whole identity as a deaf person.
A further study by Audrey Cameron, co-author of the paper with Ms Grimes, found that mainstream classroom practices themselves can mitigate against full inclusion. Dr Cameron, who is deaf, found that of seven classes observed, in three the seating of the deaf pupils was inappropriate to the point they were not sure where to look.
Pupils were restless where the staff interpreter had low levels of signing skills and pupils often missed the chance to answer questions. In one lesson, 93 per cent of the teacher's questions were not translated in time to the pupil.
"We can't generalise from this observation as it is small scale," Ms Grimes said. "But it gives cause for concern and can inform developments. While ministers are right that there have been a lot of developments to allow deaf children to participate in inclusive education, we can't afford premature assumptions about everything in the garden being rosy. There is a pressing need for continued investigation of attainment, experiences and classroom observations."
Ms Grimes will be presenting her findings on day two of the four-day congress, which is held every five years in the UK. First staged in 1975, the ISEC has become a prestigious forum for understanding the principles and practices of developing educational systems that include students, whatever their age and their need for support.
Between 800 and 1,000 practitioners and academics from around the world are expected to gather at Strathclyde University in Glasgow next week to share best practice and new ideas on inclusive education.
An overview of the inclusive curriculum in Europe will be jointly presented by delegates from Austria, Scotland and Germany, who will be promoting the European Masters in Inclusive Education as a way to improve pan-European approaches to inclusion. A selection of English academics will discuss changing approaches with children who challenge, and a Canadian contingent will talk about the power of SmartReading.
Save the Children delegates from Serbia and Montenegro, Bosnia and Bulgaria will talk about promoting access to mainstream education. Representatives from Manchester and Newcastle universities will look at the relationship between inclusion and pupil achievement in England.