Hi E.,
I was a sixth grade teacher before my daughter was born in March, and I had a number of kids who had trouble getting work done in class. Some were diagnosed with ADD or other issues, some weren't. For my kids with serious attention issues, I would set a timer and give them a certain amount of time to complete a specific amount of work (this could also be done by timing herself on the clock in the classroom). Breaking up the time seems to help. I would also give my students a checklist of assignments that they could check off as they go. If possible, it would be great if you could sit and observe in her classroom for a day. I would talk with the teacher ahead of time and say that you've noticed that your daughter isn't getting her work done, and just want to see what might be different in the classroom setting. Sometimes kids are distracted by the things on the walls, other students, which seat they have in the room, etc. Now, your presence will change the dynamic, but you can see in person how the day is ordered, what time is allowed for assignments to be completed in class, how your child uses the time, etc.
I hope these suggestions help. If I can be of any other help, let me know!
:) K.