I'm not sure if ADD is the case either because there are a few people here who has it and write pretty good. But it is very possible that most school ignored the problem because deaf education is still "experimenting" with trying to improve the 4th grade level that they associate with deafness using speech/hearing/Manual Coded English. according to overall statistic, it is still stuck on that level no matter what method they used... they need to stop experimenting communication, stabilize a language for the deaf so they can work from there and be able to distinish deaf people with learning disabilities.
and yes, parents can have alot of influence on their deaf child's language, but they can be great parents but have a child who is undiagnosed with learning disability.