You poor loves. Sounds like the school is not overly supportive.

A few questions.

Did the diagnostic team give any written recommendations? If so, are they being followed by the school?

What systems are in place to prevent meltdowns?
Is Jaycen being taught to recognise when he starts to get upset?
Does Jaycen have a "safe spot", eg the reading corner or medical room, where he can just go when he needs to?
Does Jaycen require permission to access coping techniques? Eg having to ask for a fiddle toy.
Is there home school continuity? So does the same behaviour get the same response in both places?

How do the other children respond to Jaycen? Are they egging him on, encouraged to ignore, or do they buddy up and help?

Hope those help and good luck with the discussion with the school. If they don't play nice, ask if he was excluded for his disability.