Re-evaluating the IEP seems like it may be better for your son at this point, and getting some assistance with how to do that and interact with the school successfully in that respect in important. I just wanted to mention that while you mention having tried some medications to assist your son unsuccessfully (with some terrible experiences to boot), I recently came across an article on atomoxetine (a SNRI) that may be worth considering given the impulsive behaviors that are challenging to monitor and control. My son also experiences difficulty with controlling his impulsivity as a primary problem, so when I read this article, I perked up because of the emphasis on improving impulsivity specifically.
The conclusions from the article with first author Samuel Chamberlain (BIOL PSYCHIATRY 2007;62:977–984) are below:
Atomoxetine improved inhibitory control, most likely via noradrenergically mediated augmentation of prefrontal cortex
function. These results have implications for understanding the mechanisms by which atomoxetine exerts beneficial clinical effects and suggest novel treatment directions for other disorders of impulsivity.
While I am sure another medication is not on your radar at this moment, it may be worth looking into, especially if impulsivity continues to be a focal point for some of the behavioral aspects of his ADHD.