School says not SPD but Behavioral Problems

My son was diagnosed last March with SPD more specifically sensory seeking, postural disorder and mild auditory over-responsivity. I was so glad to finally have a name for all of his symptoms. The OT said his behaviors were because of the SPD. We struggled through 2 years of preschool and now in kindergarten we are met with even more issues. He now attends a full day, which I opposed, and has been screaming and refusing to do his work.

The principal says that she has seen many sensory kids and he is not one of them. She says he has behavior issues and is trying to get his own way. Has anyone else dealt with this? I thought that a SPD child portrays these behaviors because they are trying to cope with their environment. Any comments is greatly appreciated.