My first question: Who diagnosed him with an auditory processing disorder? This person should be advising you. Such a disorder often causes learning disabilities. Was he evaluated for this?
If your son does not have ADHD, he should not be considered for an ADHD medication. I cannot answer your questions on placement in middle school without knowing more details.
If your son has an IEP that clarifies your sons disabilities and the services needed, do not tolerate any teacher acting the way you describe. Keep a log of each occurrence.