Deaf schoolchildren are falling behind their hearing peers at every stage of their education, according to new statistics released this week.
The figures from the National Deaf Children's Society (NDCS) Cymru reveal for the first time a shocking attainment gap between deaf and hearing pupils in Wales.
Last year deaf pupils were 30 per cent less likely than hearing pupils to gain five A*-C grades at GCSE, while at key stage 3 only 42 per cent of deaf pupils achieved the core subject indicator, compared to 71 per cent of their hearing counterparts.
Now NDCS Cymru is calling on the Assembly government and local authorities to take action to close the gap.
Jayne Dulson, the charity's director, said deafness is not a learning disability and there is no reason why deaf children should not achieve the same as their hearing peers if given appropriate support.
"There is frustration among many parents of deaf children who feel they aren't doing as well as they can, that they have a potential that is not being fulfilled," she said.
Data on the educational attainment of deaf children has been available in England and Northern Ireland for a number of years, but the charity said it struggled to unearth official figures for Wales.
Even now there is not a complete picture: Assembly government statistics put the total number of deaf children in Wales at around 1,400, but NDCS Cymru estimates that the figure could be much bigger.
It is pushing the government for more robust data.
Jayne Dulson said the charity has identified a number of barriers preventing deaf pupils from achieving their full potential at school.
Top of the list is a general lack of deaf awareness among teachers and support staff, a problem which the charity says can be easily addressed through training.
Ms Dulson said: "Teachers may not always appreciate the difficulties a deaf child is facing. In a class of 30 pupils a deaf child may be overlooked. We believe teachers should have mandatory deaf awareness training as part of their induction."
School buildings can also present a barrier due to their poor acoustics, with newer buildings often causing more problems than older ones.
"In new school buildings aesthetics is more important than acoustics," said Ms Dulson. "Money is being invested in building new schools and redeveloping existing ones.
"We think it should be a statutory requirement to have a pre-completion acoustics test, so that deaf children are taught in an acoustically appropriate environment. It's far easier and cheaper to do this at the design stage rather than later on."
The charity is also concerned about the wide variation in levels of support for deaf pupils across Wales, and the difficulties of recruiting and retaining specialist teachers.
An Assembly government spokeswoman said officials were committed to ensuring that all children with a hearing impairment are provided with quality education.
But she added: "Although it is encouraging to see improvements in the attainment of hearing impaired pupils from 2005 to 2008, we do however recognise that there is more work to be done."