ASL or any sign language is the rare case where there is no written equivalent.
From my experience with schools for the deaf it seems that the teachers do not believe it is important for the students to have a good grasp of written English.
Personally I think this is a huge mistake because it limits the possibilities for living in a world where the written word is often a core part of employment.
To be fair this isn't just a problem among the deaf. More and more hearing kids are graduating from high school are functionally illiterate. Texting and twitter are doing nothing to improve that.
Another aside to this is when children who are physically disabled they also seem to be subjected to this second rate education. I don't understand it. Why shouldn't they be able to get the best education possibility? When my daughter was in the reverse education program (she went for one year to a class filled with kids with physical disabilities) they warned us that they would only do this d=for one year because it did put the child behind their peers in the school they would normally go to.
But getting back to the issue of the ability for most deaf people to comprehend written English does a great disservice to them. it isn't because they can't learn. Many are smart people. But they haven't been encouraged to to have a good grasp of the language.
So I'm not just picking on the education of the deaf. There are problems throughout the educational system that need to be addressed.