Have just posted on your original thread - thought I'd better move my reply to here:
Not wanting to sound patronising but well done to you for fighting your son's case through Tribunal - I know of so many parents who just give up in the face of LEA opposition. Just wanted to add re your son needing extra time - you should have been told well in advance of his sitting not the day/night before. Children without a disability know in advance how long they have to complete their test papers, so to only find out the night before could well be disability discrimination, you would have to prove that he has been treated less fairly on account of his disability, I think that the poor invigilating (pretty apalling is an understatment) could certainly strenghten you case.
I agree with Patricia and Sally-Anne, log your disatisfaction now, and given that he has a Statement, write to your LEA as well as the school,you may want to contact the disability rights comission for advice also.