I'm so sorry. Advocating can be so incredibly stressful (says the woman who has only had one teacher meeting) and it's so hard to do since there are so many variables.
Can your sons father help you out? Or maybe a well spoken friend? Can you write down all of the points you need to address and use notes during your meetings? Has the school seen his test results? Can you make them a binder with his results, his work, a sample of what he reads, etc?
Hang in there!