I am dyslexic and I used to have bad tantrums concerning all school work, even art. This was due to the fact that I could never get out what was in my head effectively down on the paper. I would make silly mistakes or it wouldn't look like I wanted it too or it wasn't perfect enough.
It resulted in many screwed and ripped up school projects. With time I eventually found a way round doing certain things and the tantrums faded. All you can do is be there to say never mind, try again.