I agree with the poster who suggested asking an independent professional to shadow your child in class then arrange a meeting with the professional, the class teacher, sen staff and anyone else normally involved in meetings planning to meet your child's needs.
My son was diagnosed with ASC when he was six, as part of his diagnosis process, his psychologist shadowed him throughout a normal school day. Including break times. My dh and I requested referral through our gp, my sons then school didn't think he was autistic, labelled him as 'naughty' and as a result rubbished our concerns about our son. Having the psychologist visit the school was not only life changing, it forced the school to recognise our sons difficulties. For example, during break time the staff believed my son was screaming and deliberately chasing and running into other children. They believed he was getting pleasure from this because he had a 'smile' on his face. In fact, our son was in a state of sensory overload, his brain had gone into 'flight mode' and he was running terrified. His heart was racing and he was sweating through fear. He has no idea where his body is in relation to other people/ objects , which is why he was running into people, he screamed because he was terrified of the noise in the playground and vocalising allowed him to concentrate on his own noise! He was smiling because he had a limited range of facial expressions. It took a psychiatrist one day to see what we had been concerned about for years!
Within the classroom my son was stimming and vocalising because he was completely overwhelmed by the noisy, bright classroom environment. He stimmed to calm himself but was repeatedly told off for this. His teacher thought he was being silly/ deliberately distracting his peers when he rocked back and forth on his chair whilst covering his ears. His psychologist was able to explain to my sons teacher that he was behaving this way as a coping mechanism. I could have spent time observing my son and explaining his behaviour, however I know that they would not have listened to me, let alone believed what I was saying.
If your sons psychologist/ specialist is unable to/ too busy to visit your sons school, contact a charity that deals with your child's disability. The year after my son was diagnosed, he was placed in a class with a new teacher. We were having the same issues as we had the years before, so I contacted the national autistic society and the last who ran our local branch volunteered to visit my sons school and observe my son then explain his behaviour to his new teacher. She then offered to run a course on autism for firstly the staff at school, then for parents of all children in the school. This was fantastic and I cannot praise the NAS high enough for their support. Unfortunately, the school were good at making promises but really bad at following them through. We chose to remove our son from school and we have home educated for the last two and a bit years. This has proven to be fantastic for our son and he has progressed way further than we ever dared to dream!