My best friend when I was growing up was ( and still is, you don't grow out of it) dyslexic. He was shoved down into the bottom sets and was alienated from the learning process until his situation was recognised. I remember the first time he took a maths exam with his dyslexic tutor, who read the questions to him and took down his answers. The next term he jumped from set four to set one and ended up leaving high school with ten GCSE's. If he had been penalised for his English comprehension, I have no doubt his only qualification would have been his B in Art. Grammar is important but it is also important to recognise that English is not the only subject, and bright, capable pupils should not be written off, not everybody processes information in the same way.