In our daughters 6th grade this was the main focus of the first semester. EVERY student was to follow a protocol about staying organized.
Each child was given an academic agenda (August - May).
They were to have a different colored folder for each subject and label the cover and place their name and name of the teacher on the front (in case it was found it could be returned to the student). On the inside left flap they were to write "homework", on the right side "completed home work".
They were to have a plastic accordion file large enough to hold their papers for all subjects. Name placed on the front with the copy of the students schedule on the little pocket in the accordion file. They were to label (tab)each pocket with each subject.
In the agenda for each semester they were to write their schedule in the agenda with the subject, classroom and the teacher. There was a special section for this.
Each day as they walked into the classroom, homework was to be turned in the moment the student walked into the room( there was a homework box, just inside the door). The teacher did not remind them, they were to do this on their own. As they sat down, written on the board was the homework due for the next day they were to list this in the agenda including the subject. Each student was responsible for writing it down the minute they sat down. Any notes taken during the class were to be dated and placed on the "homework "side of the folder. Any school correspondence.. letters from the principal, teacher, etc.. was also placed on the homework side so the student would remember to give them to their parents. That evening as the homework was being completed they could refer to their notes.
Once the home work was completed they were to place the homework on the completed side. The notes were to be placed in the correct area of the accordion file. Any graded homework was to be placed in the accordion file under the subject.
In our daughters middle school, they did not use the lockers. The reason? Because this way the kids had all of their folders and files all with them at all times during the day. Copies of each subject text books were sent home at the beginning of the year and each classroom had their own set.
What our daughter discovered was at the end of 6th grade, she did not need a folder for each subject to stay organized, she did need the agenda and in college she still uses it as well as her laptop.. She liked the accordion file and continued to use this as an organizer all the way through high school.
Your son needs to figure out what works best for him. He needs to own his organization. You can guide him, but he needs to figure out the easiest way for him to not become over whelmed. collecting the information, hanging on to it, completing it and getting it back to the correct teacher. Let the teacher/teachers know you are working on this with him.
I would speak with the school counselor about how the school can help your son find a way to stay organized. Maybe a resource teacher or an "in school tutor" or mentor. If you feel you have really tried everything, DO consider all options, medications being one. Your son needs to be at his best to be able to do well in school. There is no shame in this. You have a chronic condition and I am assuming you take medication to get through the day? If your son is diagnosed as ADHD this will never change and he will never grow out of it. Adults with ADHD have to be able to work and be organized to keep a job. My husband is ADHD I have known him since he was 13 and we have now been married 30 years. It is still something he deals with on a daily bases. He has found coping skills, but it is exhausting.