Retard in a Wheelchair

I wanted to ask your advice? If you knew that a child in a secondary school had been handed back his homework with the teacher's following remarks written on the work, how would you feel / react? 

"This is the kind of work I would expect from a retard in a wheelchair." 

I am not exaggerating when I say I have thought about this shocking and seriously ignorant comment every day since.

Yesterday, I was lucky enough to be invited to spend time at Helen House Hospice and today I have been listening to some incredible stories on Jack FM from exceptionally brave children and parents telling of their amazing experience at Helen & Douglas House. I was moved to tears, particularly by hearing Kathy talk about her wonderful wheelchair bound son Josiah. Skye too was wheelchair bound but as many of you will know, not for one second was he treated as 'less of a person'. It was listening to these stories today that has precipitated me writing this post.

We have had some appalling remarks made to us about Skye since his death on our brain tumour awareness You Tube videos, such as: "What did he die of, the fat face disease?" and "He is better off dead with such an ugly fat face." These comments are malicious and I genuinely pity the people who have nothing better to do than to write them. As a family, we chose to put ourselves in the public eye in order to try and guide and educate even a few people about the challenges facing children diagnosed with cancer. We accept not everyone will be supportive but it feels right to help where we can. These comments, I can shrug off.

Am I over reacting to this teacher's written words, or do others find this comment wholly unacceptable? I would like to approach the Head to discuss the matter but don't want to be considered a 'trouble maker'.