I am so sorry that you are feeling that way. We have been a montessori parent and still are and we have found that there are a lot of challenging stuff around there which your son can do. My older DS enjoys it thoroughly so as my younger DS. The older one was reading when he turned 3, few months after we started school and younger one who is in preschool is already doing addition and reading CVC words (he is a bit slow in reading and good in math). We have hardly done much at home with the older one and none at all with younger one and have really been impressed with what they are learning at their montessori school.
I think that your son's school is either not montessori or your son needs a more directed approach to learning. Many schools go by montessori label but do their own thing, so watch out for that. The teacher is not clicking with you too. I'll either move him to a new classroom with a new teacher if thats a possibility or change schools or homeschool.
Thinking about him saying, the work is too easy might mean it is not interesting as well. In our house its a different story with our preschooler- he says I can't do it, its too hard when he doesn't want to do it but when he is in mood then no complaints at all.
If I were you I wouldn't rely on testing to tell me whether my kids are gifted or not. If they are not as per the testing, they still will be gifted to me in their own ways, afterall a test is just a test. Its how you raise your kids, that matters the most.
I hope, I didn't write too much but keep an eye on the school and see whats clicking and whats not.
