Try to break down step by step what the missing link is…
Does he not know his assignments? (Planner and planner checks)
Does he not have his materials? (system to get the materials home)
Does he get home and never start? If so, what is he doing with his time? (visual schedule, timers)
Does he start, get frustrated and quit? (academic support, how are the notes? does he reference resources?)
Does he start, take a break and never come back? (Timers and schedules)
Discipline only works if he has the ability to complete the task.
If there is a specific breakdown that you can identify, the best follow-up plan will address the area of the breakdown. (See ideas in the parentheses).
Basically, we use external supports to help with the executive functioning that he is lacking.