There are many accommodations and modifications that could be in place for your son. His behavior is a significant change from his previous years. As a school physical therapy consultant, i have incorporated movement related accommodations and modifications in the IEP ( if it’s not in the IEP, it’s not being enforced) including alternate seating systems like a ball chair, air filled seat cushion. However, there are a lot of things to consider before the final accommodations are finalized upon. eg- how does your child, teacher, peers view the accommodation. Teacher buy in and peer awareness about the need for an alternate seating system is critical for consistent implementation of an accommodation.
Feel free to email me at firstname.lastname@example.org me if you need help navigating the school process in getting adequate support. There are some movement related activities that you may want to incorporate everyday too. Hope this was helpful.