Rolf, I can give you an answer to your question.
Karaoke does help to teach people with learning disabilities. On my saturday at a family pizza place, I have a 42 year old with what would probably be called autism today. A year and a half ago when he first started comming, he couldn't keep up with the pace of any song, and only sang key words or phrases, and mostly danced shaking it the rest of the time.
Now His reading ability is much better. He keeps up with the pace much better on all of his songs, His reading is just bettter. Now he stays silent a lot less often, and talks the song most of the way through. Bottom line practice in a fun way has definately worked for him. He graduated high school back in 85, so I hope his reading was at least alright, and the skills just disappeared due to lack of using the skills.
Hope this helps,
Felix the KJ