I’m assuming you have an IEP in place with his school. The one thing that has helped us the most with my child’s behavioral issues is placing him in an E/BD program (Emotional/Behavioral Disability). If your county has this program, I’d highly highly recommend trying to get him placed in it. It is made for children with ADHD, Asperger’s, ODD, and behavioral dysregulation.
In my county, the classes are mixed (K-1, 2-3, 4-5) and small (7-10 kids at most) and there is a teacher, assistant teacher, and 2 behavioral techs, plus a quiet corner and a whole other private area with dimmed lights and sensory play to “chill out”. We get detailed behavioral reports sent home every day with scores per hour and activity for several behavioral goals. The idea is to move him through from stage I (basic behavioral goals) to stage 4 (advanced) and eventually reintegration into a normal classroom setting. Meds have helped some (Ritalin), but this has helped even more.