If a written assignment isn't truly necessary, don't assign it. Use that time for more engaging activities and collaborative group work. Even the most traditional activities can become more engaging with a little bit of extra thought. Remember that children, even children with ADD, will be more engaged when they are encouraged to play active roles in the learning process. When you have students with ADD, really understanding your students becomes even more important.
Every child has something that they find exciting or interesting.
It might be hard to figure out, but it's there. Sit with them at lunch. Invite them to help you after school. Building a positive relationship with that student will help you understand them as a learner, and it will also let them know that you really want them to succeed. He was all over the place.