He sounds a lot like kids I've taught and in some ways my own DS7. A few thoughts...
Montessori uses the step by step method of instruction. This is, show me, what is this. Each lesson uses that basic format. Once one lesson is mastered the next in the series is then presented. It is very linear and depending on if you are dealing with an AMI or AMS school can be a challenge to change.
Having said that many lessons are actually already compacted and accelerated in the very format in which they should be presented. Addition and subtraction should be presented very early on with 4 digits right away. Exchanging lessons are usually done early as well. Many different skills can be presented along side each other. I remember my then 5 year old working with addition, fractions, multiplication, and geometry all in the same week.
The problem may be coming in the fact that your son hasn't been in Montessori since he was 3, which is when they usually start. So for the teacher she is trying to teach him using a method that normally starts at age 3. Even accelerating would take time. For example if he hadn't ever done the knobbed cylinder work which would usually be done at the 3's and 4's she may feel like your son needs this. This work can look like a waste of time for him, when actually it is teaching a child many things including proper pencil position and the feel of different weights for later weight lesson. It reinforces visual and spatial skills as well. Or she may have him doing the long bead chain which is time consuming and he may complain in doing it. It is really multiplication through skip counting, concentration work, fine motor skills ect.
The other thought is the concentration that Montessori teaches. For a gifted child whose mind is going a million miles a minute, the Montessori method can be a challenge. I know it was for my son. He was asked to slow down and do things step by step to completion when his mind was 5 steps beyond that. For the 3-5 years ages we loved this. It forced him to start to train him mind to do what he wanted, not the other way around. A huge task for a gifted kid. Maybe your son is experiencing the same thing. That training of the mind to really concentrate has been a blessing for my now DS7.
One last thought. You may ask your child what interests him in science or social studies and see if he can do a big project on it. Montessori allows for big involved research projects. He could type it or do a powerpoint if writing is an issue. This would give him the break his mind needs. Slowing down and doing things step by step can be mentally, emotionally and physically exhausting in the beginning. With a project he can think 5 steps ahead, map it out, play with options and come up with great results. It could incorporate higher level thinking skills, higher vocabulary, math, graphs of results, drawing or art. The possibilities are endless. Usually one or two weeks on the same project is a good place to start.
Hope that helps! Good luck
