I just wanted to say that I feel for you and to hang in there. You are not alone!!
Our little boy is in Pre-k and is 4 at the end of the year. We are based in Australia so he's been in his class since feb. The teacher pays little attention to his giftedness and st the first parent/teacher conference we had the whole 'he needs to comprehend the story not just read it' 'we are working on counting to 3 in class'
He was tested a few months later and we have had confirmed that he is gifted, how gifted still remains a mystery as he ceilinged the test at only 3. So we certainly know he is at least highly gifted.
The problem is that he is 2e nd he doesn't show any of his amazing skills and talents at school.
We have not pushed at this stage and have allowed it to just be left unacknowledged but are pushing for extension with the principal for next year.
Have you tried meeting with the teacher to talk through exactly what his IQ tests mean? For us I think that was quite important and made them stand up and take notice.
I wish you the best of luck