You have a lot of great advice above, so I don't have much to add - but here are a few thoughts.
Sometimes at school you hit a brick wall in the form of a teacher or other staff member - they aren't going to give no matter how you advocate. They might have become a brick wall for any number of reasons from someone above them telling them "no, our school can't do this" to simply being tired, overworked or not caring. It helps to figure out (if you can) what might be driving their unwillingness to help in order to make a game plan of how to fight it... or to know whether or not continuing to advocate is going to help.
Your school must be willing to subject accelerate as a policy since your ds was accelerated last year. You've had 5 parent-teacher conferences already and it doesn't seem to have helped. Is anyone else getting called into the meetings by the school? If not, I think I'd approach this meeting with a plan - take a written list of what accommodations your ds was given last year (he was subject-accelerated in math) and the dates of conferences you've had this year with what was agreed upon at each. Point out what hasn't happened. Ask what will be done to resolve it. Let the teacher know if what you agree upon doesn't take place, you will call a team meeting (don't know what they are called at your school - but it's the type of meeting where the teacher, parent, counselor, school psych etc all meet together to discuss the needs of the student). Most often those types of team meetings take place when a child is having a difficulty which has to do with a learning challenge or behavior challenge, but if your child is feeling that his teacher thinks he is stupid and isn't getting the work he's capable of doing (particularly after already having been acknowledged of being capable of higher level work by the same school) then you have a very valid reason to call a team meeting. If you have to have a team meeting, I'm guessing you'd get what you need there simply because the school gave your ds his math acceleration last year.
Re crying, emotion, etc. I've never cried at school - that's not really my personality. It's also my nature not to want to make waves, be confrontational, or make demands. What I've found works effectively for me sometimes is to simply state the obvious, and repeat it when it's not heard. The school staff may try responding, backpedaling, getting off track etc to not be pinned down on something but just simply repeat the very obvious points that your ds is entitled to - or ask why not. Repeating with slightly veiled sarcasm can work very well too. But before I tried any of that, I'd first do as mentioned above - put together my very specific list of what my ds needs (subject acceleration) and a starting point of a suggestion that you're willing to settle for in terms of how he can get it, ask for that first then go from there.
If the meeting doesn't go well or if the teacher doesn't follow through - request the team meeting (in writing, email is ok), and be sure the principal is cc'd on the request.
Good luck with the conference -
polarbear
