I am a Speech language pathologist and work with children with ADHD. I usually work in a multidisciplinary team which includes an Occupational therapist. I think that your son could benefit from an OT assessment focusing on sensory integration function and processing The therapist could help figure out what triggers these outbursts, but then should help educate you and the school staff on triggers but more importantly solutions. A good OT should be able to also help your son recognize triggers himself and help him become self aware, and responsible for himself as time goes on. The OT could probably help you with educating your husband and help “get him on board” as well. I often see this in my practice (husbands reluctant to see the problem), however with good team work,
(You, your son, the teacher, OT, Dr,and other “team members) you could all help educate your husband and eventually he will join the team and thank you for years that he did. Look up an approach called “cogfun” and see if there is a provider near you. If not, see what might be similar. there is also another multidisciplinary similar type of treatment designed for autism, but based on the same model – Floortime – Dr stanley greenspan and Serena Weider – they have an excellent website.