Do not attend this meeting or any meeting alone. You are his parent and we don't always think rationally when they are addressing our children. Your medical documentation is enough information to obtain a IEP or 504 plan. An IEP can be written on a health or physically impaired diagnosis (HOPI).
I would recommend that you have written into the IEP time during the day for him to get out of the classroom and taken to the gym and run or have some physical activity.
Sometimes going to the resource room is just down time for students with ADHD that need to relax and find that encouragement in a small group.
I would also recommend with the end of the year coming quickly to an end. Go and visit classrooms for next year meet the teachers, talk to parents, and request a specific teacher based on your child's needs. Academic structure, classroom management, etc.,
Be that advocate for your son the more you do it the more confident you will become. Do not take no as answer just ask the same questions a different way. Do not allow them to tell you about your son, tell them what your son needs are.
Look at what he needs for academic progress tests taken in a quiet area, tests read to him, maybe he needs to read the tests out loud to himself.
Look at him as a whole not only his ADHD.
Shel
If your not kicking hard enough your not making waves!