did the actors need to learn to sign??

Yes to my knowlege all the actors in this movie are deaf and use asl. Marlee matlin herself is deaf and uses asl. I say this because I can tell by how the kids prounce their words they sound as though a deaf or hard of hearing person would sound.

wow way to be a jerk, drunkdaddy...

the answer to the question is yes, Hurt had to learn sign language to play this role. Here is a quote from the NY Times, and the article link:

"Because the part of Sarah is played by Marlee Matlin, a deaf actress, and the students are also portrayed by people with hearing problems, Ms. Haines and the co-screenwriter, Hesper Anderson, as well as Mr. Hurt, had to learn sign language. ''To direct, I used what is called 'total communication' in the deaf community,'' Ms. Haines said. ''That's whatever works - gestures, body language, lip reading, signing and full-time interpreters.'' "

http://query.nytimes.com/gst/fullpage.html?sec=health&res=9A0DE5DB1530F935A1575AC0A960948260

How in the hell is someone born knowing how to sign you idiot?

I didn't see that as a plot-hole at all. I took it to mean PL played the part of a single overworked mother with somewhat of a chip on her shoulder who never did learn ASL very well. She signed as if she did "just learn a little bit" and barely could communicate with her daughter. She admitted they didn't talk because her daughter didn't want to talk to her, and she was tired of folks coming by every so often to talk about her daughter and, in her words, to blame her for her daughters volatile, somewhat rebellious nature. I thought she played the part perfectly.

Thank you for sharing. You described your teacher and his abilities very well. He sounds fascinating.