Without making any judgments about the school, or the parental assessment of the school, it strikes me that there may likely be a much simpler short term solution, given that the OP indicates that a resolution will not be available for her son. Change schools. There are private options. There’s homeschool (as someone already mentioned).
@bh2021, I’m don’t think that it would be of any benefit to your son’s future college admissions plans to embark on path of trying to convince “Top school” or any school admission officers that for four years of high school, the teachers caused your son to have a lower GPA than what his potential is, and lower than other kids at his school. As another poster already mentioned, college admissions is about performance, not potential. And, by the way, your son has not performed poorly. 
His classroom performance, with Bs and Cs is average. His co-curricular performance is outstanding. And, there are many, many colleges that would admit him, and give him merit for his 34 ACT. Most importantly, he has another full year to demonstrate that his academics are on the rise, before beginning to apply.
No matter what you decide for the rest of his high school years, I promise you that he will have options, and good ones, for college. But, you may have to adjust your perception of what “top school” means. In spite of national lists that rank colleges, “top school” is in the eye of the beholder. First and foremost, it should always mean “fit for purpose”. Prestige is not a measurement for “fit for purpose”.