Help! Calling all Student Behavior Experts!

Ladies (and the occasional gentleman), I need some help. I have spent the last week in hell. There is really no better words for what this week has been.

I feel that a critical problem in my school district is the follow through of discipline. I have just transferred from 1st grade to 3rd grade this year after 3 years on the primary campus. I have grown used to a principal who does not believe in corporal punishment and we have gone through 4 different mash-ups of school wide discipline/management programs. I have watched as year after year the students become rougher and more violent. They are prone to outbursts and are physically harmful to themselves, teachers and other students.

There is one student in particular who I am "blessed" enough to have in my 3rd grade class this year. I have watched him year after year get away with being coddled. The school implemented a behavior improvement plan in the hopes to aspire him to be a better student and to give the teachers some guidelines to follow. So far within the first week of school, I have been screamed at, my personal belongings have been thrown across the classroom and I fear for myself as well as the other students around us. I have gone to the principal and assistant principal every day, sometimes more than once. I have already had one parent conference with another scheduled for Monday and I have already discussed classroom evacuation plans with my other students. The student was sent home from school on the third day of school due to being sent to the office 3 different times throughout the day.

My question is, When is it enough? Is there a point that you just give up on educating a child? How can you teach the other 20 students in my classroom when we are terrified and drowned out by the voice of one student? Is there a classroom management system that works? How enabled is this child by the parent and as a public school district what can we do to protect the other students and teachers from being harmed?

I wonder as educators, what would you recommend in the situation and at what point would you say that enough is enough. I have already asked to have this student removed from my room but none of my requests or suggested changes have been implemented.

What do you suggest? Do you have experience with defiant and belligerent children? What can we do to work on some problems?