Hi.  I agree that classes which mix literacy students with more  
advanced students are really difficult, in part because literacy  
students need more attention and can do less on their own.  Linmore  
publishes some beginner books (they have a website) which have very  
structured exercises (they look too easy unless you are a literacy  
student) and may be usable for some literacy (or maybe literacy plus  
a little) students while the teacher works with others in the class.   
The teacher would need to work on the story with the students first.   
They have some for teenagers as well as adults.  Abbie Tom