Hi V.,
I'm so sorry you are going through this. I hope you all find some peace and can move on soon!
I agree with Martha - he definitely should qualify for an IEP. In some cases they have an aide that actually stays WITH him during transitions and can 'talk him down' when they see warning signs (if there are any) so that you don't get a full escalation.
I think in this case especially (because you know there are special circumstances) you want to limit PUNISHMENT and just focus on DISCIPLINE with natural consequences. So, he wouldn't have stuff taken away from him that doesn't relate to the infraction (ie if he throws his DS, it's taken away.... but he wouldn't have his DS taken away for throwing a fit at school). Additionally, I'm curious if taking stuff away might be a trigger..... it might especially remind him of when he was taken by his dad and lost you and the stuff he loves.
If you can do discipline and natural consequences it might work like this..... his natural consequence to running away at school might be to write his teacher a letter to apologize each time he does it (therefore he will have less time with his toys - which he won't like, but it's different than punishment).
One question - does he have an appropriate outlet where he CAN express his rage? Like a physical activity? Tae Kwon do is fabulous - or even something like kickboxing or swimming where he would have to be super physical would help him channel that extra energy in a positive and controlled enviornment. All of those activities build self-esteem and the coaches are usually great role models - any additional adult role models he can get that are positive would be good for him.
One additional note.... it sounds like (and I might be guessing) that some of his issues might be control issues over not having control over his environment...... that's something that a 6 year old who isn't in the middle of a nasty divorce with a disruptive dad would struggle with.... for your little guy it must be maddening. Are there (appropriate) things you CAN give him more control of? You don't really mention if that's an issue..... but if I try to peek inside his mind I could see where it might be. When I went through my divorce, my daughter got kinda freaky.... so I started letting her have total control over things like what she wore and what sheets were on the bed and what lights were on in her room at night. I also started letting her make some choices 'should we have chicken or porkchops tonight?' and I found that the more decisions she got to make the calmer she became. NOTE: not everyone believes in this, though... kids making decisions.... so check with your therapists to make sure they are on board. Some kids might not want or be ok with all that responsibility - it made my daughter thrive, though.
One other suggestion - and I know my reply is long...... have you asked your son to brainstorm ideas about what ELSE he could do when he feels like running away? or when he feels like screaming? It might be a good idea to make a list so that he has some behaviors he knows he can do that are ok..... like "when I feel like screaming.... instead I will turn 4 cartwheels" and "When I feel like running away..... I will color an entire piece of paper with a red marker". The school would have to be on board with 'alternate activities" but I would image they would want to be creative?????
also - have you validated that it's OK for him to feel how he feels.... that sometimes you want to scream too? I think that might help him as well.
I know his behavior is way out of control and it may seem to you that if you punish him he will control himself. But 6 year old under the BEST of cirucmstances still struggle with impulse control and your little man has had a big whammy with inconsistency and trauma. So where you could expect to tell a child who hasn't had his experiences 5 times you may have to repeat yourself 25 or 30 times with him - and that's OK.
Good Luck!