Hello, in my experience, it's a very long road which you will need to fight his corner every chance and you will grow a very thick skin.
The school report will work to your advantage to push for assessment. The teacher is being factual (not helpful to your son, I know)
Ask to speak to the school for pastoral care plus SEN. In regards to sitting alone, we had the same sort of thing by sitting her near the teacher or at the front to keep an eye on DD.
DD needs to be at the back so she can see the door and other pupils and needs her routine. It's not rocket science.
At one school meet the teacher, the art teacher complained she had put dd near the sink with paint, pots and glue which caused dd to lack focus and concentrate more on pouring glue and paint everywhere.
It did take a very long time to get diagnosed and proper help in place, I lost a job over trying to support her in (or refusing to be in) school.
DD left school in the first lock down, passed all of her exams and her school reports blew us away. There is hope, your son is lucky to have you posting here looking for help so early in his school journey. Keep posting and stick to your guns!