It's great that the school goes all the way up until 8th grade, that gives you some wiggle room. Sign up for a placement test on ALEKS.com say at a 6th grade level and see how he does. Then you know what to ask for in Math.
Did the teacher move him up in reading? It's possible the tight face was because she felt 'tricked' or 'set up' by your son, and then wanted to correct the error ASAP.
Some families send the kids to different schools. Some families are able to really provide the leadership of 'we are all on the same team and cheer each other on' it sort of depends on the circumstances.
When the teacher whines about accuracy, just smile, nod and then say that when you observed him doing Aleks at home, his accuracy improved as the challenge level increased. Say that many advanced kids are like that and that are proposing the higher level work because you want your child to have the same chance to develop work ethic as everyone else.
What seems to work well is to propose a 6 week trial of the subject acceleration and map out objective criteria for if it is or isn't working in advance.
Best Wishes,
Grinity
