I can understand your feelings. Working with an ODD Child is extremely frustrating.
But you may be expecting too much too soon. A new system at school has to have time to take effect. Even with a normal kid, experts say it takes 3 weeks of immediate, constant reinforcement to get a change. Neither you nor the school should expect things to happen right away.
And the trouble with sharp kids is that they work the system. They have learned through trial and error that If you don't think something is working, you will move on to another method - and they win again.
Have you talked with the counselors about your methods at home. It may be that you are trying to do to much all at once. The problem with a reward chart at home is that it can cover too much ground and the while the child may do some things he fails at other things and then gets no reward for what he has accomplished. Plus, many times the reward is delayed as well as the punishment - which effectively ruins the idea of immediate consequences. Frankly, I have never really liked this kind of a chart for kids with difficult problems.
I also am wondering if you or his doctors have looked into ADHD? Something like 35% of the kids with ADHD have ODD and it makes treating the ODD so much more difficult. This is a good link that takes a look at ADHD and other disruptive disorders -
While you didn't give a lot of his symptoms, I get the feeling that anger management is one of his major problems. This is a very good article that not only looks (again) at Anger Overload and Anger Overload and ADHD. But more importantly it gives treatment techniques for parents and teachers that perhaps you haven't heard about.
The link is - http://www.chadd.org/Portals/0/AM/Images/Understading/AUG01AngerOverloadinChildren-DiagnosticandTreatmentIssues.pdf
And besides all the consistency things - which are difficult to do - some things are easier and can be fun. For example there are a series of books that are aimed at the 4 to 7 year old. Look into buying "Cool down and work through anger" or "When I feel angry". This is part of a series of books aimed at 4 to 7 year olds and meant to be read to them at night (several times) and then practiced. Kids do need to be taught how to deal with anger. You do not try and use these techniques while he is screaming. But once he stops or later on in the day - you can refer back to them or pull the books back out.
You can find them here - http://www.amazon.com/Cool-Through-Anger-Learning-Along/dp/1575423464/ref=pd_sim_b_5
I hope some of this helps. The main thing is don't get down on your self. If this was easy, I would not be writing 4000+ posts here and on the ADHD site http://www.medhelp.org/forums/ADD---ADHD/show/175.
; This is very difficult to deal with and ALL parents have trouble doing so. And it kind of sounds like you are going through this alone (?) which makes it even tougher.
By the way, what kind of doctors are involved in the diagnosis/treatment and did they discuss ADHD? Best wishes!