I know a week feels like a long time at this beginning of school time, but if he's just had MAP testing, the teacher is planning to change things based on it, and you have meetings scheduled in three weeks, I wouldn't push for a meeting before that. What I would do would be to go to that meeting well prepared and maybe at it, ask for a longer meeting in the next week or so, if (as here) the ordinary parent-teacher meetings are too short to have a real discussion. It may be that the teacher will get a handle on your son between now and then, and you need to give her a chance.
It was about this point of his first term at school that my DS started saying maths at school was boring, and we started his Sum Folder at home. We let him ask for a sheet of sums when he wanted one at home; he could specify the type of sum, how hard he wanted them, and how many, and we'd produce exactly what he asked for. He loved it - it helped with the frustration of not yet getting maths work at his level at school - and it gave us examples of what he liked doing to show his teacher. I think it's fine to respond to expressions of frustration by telling him you have a meeting with his teacher coming up, and asking him what he'd like you to say or ask, too. Obviously it isn't for him to come up with a plan, but he should know that you hear him and there is a system for parents and teachers to work out how to meet children's needs.
