For me, the diagnosis fell out of what the teacher was doing to DS when he was 10. She genuinely believed that she could bully him into writing better. I spoke to her about it, told her I'd support her if she was willing to help him write more quickly and more neatly, and she replied something about it not being her responsibility. Then over the next few months, DS got more and more anxious and tearful, and finally he showed me some of her written comments, and told me about some of the things she had said to him.
So, I found a handwriting tutor. The tutor spent approx 10 mins with DS before telling me that she strongly suspected a SEN and asking if dyslexia runs in the family. I then paid for a private assessment and dysgraphia was confirmed (along with a high IQ and extremely good memory).
I told the teacher. She refused to accept it. She continued to make DS's life a misery. I asked for a meeting and she gave me an appointment 3 weeks away. Finally, there was a day when DS was in floods of tears in the car coming home from school and I called the HT as soon as I got in the door. I don't think I've ever been so angry in my life. I told him what was happening. I told him that the teacher was breaching the Disability Discrimination Act. I told him i had evidence of her bad behaviour to DS. And I told him that DS himself was calling it bullying. Finally, I said that if it didn't stop immediately, I'd be withdrawing DS from school (he was about to sit SATS and would get 5s and 6s) and I'd devote myself to pursuing an official complaint against the teacher, and the school for failing to deal with her.
It stopped immediately. The teacher added positive notes to the end of her comments in his books, lost others and tippexed over the rest.
All was quiet for a little while, and then, unbelievably, she started to attack me. In front of another parent, she implied I am a bad mother and that she had to do my job for me by giving my 10 year old son a sex education.