The key is for him to write down the assignment while still in the class. One thing he could try a tracking sheet, separated by class period, with a space for him to jot down the assignment and also a prompt to turn things in. (I have a created a free one on my site)
The biggest thing is he can’t rely on memory to remember at the end of the day what was discussed 6 hours before. A tracking sheet will work if he gets in the habit of filling it out each period–before the next one starts.
You could even add to his IEP that the teacher checks his planner at the end of class to make sure he knows what the assignment is and how to do it.
The bottom line though is that this is his deal. You can “lead him to water”, i.e. Offer some suggestions, but you can’t make him help himself. The motivation to change or try new things only comes when the pain of staying the same is too great. Until he sees that his actions are not getting him the results he wants, he will have no incentive to try new things. It’s hard, but it’s important that after you offer suggestions, you back off and let him take over (or not; his choice). Remember that him feeling the sting of the consequences of failing and “forgetting” is a good thing for his growth.
Parenting Coach, school counselor, author, mom of adult son with ADHD