JJJ,
You need help from your school to GET him there. You should not be driving him at all under these circumstances. Not safe for anyone.
There are basically two schools of thought on school phobia:
Get them there no matter what--and no matter if they do nothing once there because the longer the phobic object is avoided, the more intense the phobia becomes.
Address the anxiety first and then the phobia will diminish because a phobia is anxiety really exaggerated.
I actually believe both of the above statements are true for some kids some of the time--which makes Tx decisions really hard. It is gut-wrenching to have a kid go to school in full-restraint on a bus and be dragged into the building. However, it does diminish the phobia after a while. Some children who are allowed to avoid for a long time, i.e., stay home, never make it back to school at all.
There is another issue that you raise that rings a bell with me: you indicate Tigger is liked by staff because his outbursts are out of character. I had the same situation but in middle school, ex-difficult child's problems were seen as willful and he was punished in many subtle and not so subtle ways (very different from el. school.) I firmly believe that his ODD emerged as his last ditch attempt to manage his own anxiety and depression. All he could say was, "NO!!!" At least that stopped the anxiety cycle for a while for him and got everyone else going.
The reason I say this is ex-difficult child was a very nice little boy and he is very nice now. He is not "basically" ODD, but pushed far enough, and despite medications and therapy, he really had no other options to try to save himself. It is one of the hardest behaviors for schools and parents to ignore--so it a sense, school phobia "works" for the child.
I do not have any specific suggestions but I thought I would share these thoughts with you. I know it isn't easy.
Martie