I would like to share with you that I have been and ADD student since I have ever remember. However, I was exceptionally top in my grades and schools. I think what made me so successful was my interest and understanding overall to the subjects. Moreover, the relationship between me and my teachers played a very important role paying more attention.
After all, I would say, I do have ADD still in my adulthood and I could find ways to concentrate. Ways are like: listening to the music, freedom and not pressure, doing tasks which I have interest reinforcement.
I think you may want to make a good relationship first with your students. Then encourage them on their tasks and reinforce them when they are good in paying attention.
There are other ways of course which might be differ to the individuals.
All The Best