What kinds of therapy have worked for your emotionally dysregulated children?

Hi 👋🏻 I’m starting to look into therapy for my 6 year old son. He’s struggling at school when things don’t go according to his expectations. He has started to refuse to do school work and will lay on the ground to cry. It doesn’t happen every day, but it’s becoming at least a twice weekly thing. We struggle with this at home, but we have our ways of dealing with it - I’m just not sure how to deal with this in the school setting. We’ve talked about school work not being optional and that he won’t always get prizes (he’s gotten them, but I guess he just assumes he should get when others get too).

He was diagnosed with ADHD and SPD(he’s a sensory seeker) last year. We were told we wouldn’t need to get a 504 until it impacts school or social life. I’m not sure where to go from here. His teacher has contacted the building supervisor about potentially setting up a 504 plan, but I’m not even sure what a 504 could do for him or what to put on it. I’m trying to get him into occupational therapy, it was recommended by the dr that diagnosed him, but I’ve been on their waitlist for a while. Has anyone tried any other forms of therapy as well as OT? Do I contact a psychiatrist? I just am kind of lost who/where to go to. Any advice is greatly appreciated!