Assuming that the entire group of pupils is following along with the lecture shows a strong sense of disregard for your students as a whole. Also, getting frustrated about the situation does nothing to solve the issue at hand. If anything, it would probably cause the student to feel worse about having to alter their surroundings in the first place.
Not everyone can pick up and learn things at a fast rate. With that being perfectly fine, we also all have to eventually adapt to the different environments and people around us. Why is that difficult for some professors to do? Is it too much of an inconvenience to write larger, to repeat something you've just said or to speak a little louder? Is it too much trouble to ask if there are any questions or to not speak with such fast, slurred sentences?
Constantly belittling a person for something they cannot help, would ultimately cause them to stop asking for help. Dismissing the situation does nothing for the professors' credibility because "No one has ever made himself great by showing how small someone else is" (so says Irvin Himmel).
No one should feel burdened by their disability and these people are entitled to the right to learn just as much as someone without a disability. Yes, it is their choice to speak up, but the fear of being reprimanded keeps their lips from parting.
As an alternative, I personally recommend changing your outlook on people with disabilities altogether. In some instances, they have the same capabilities as an able-bodied person. All that is needed is an extra push or a change in approach.
Encourage questions and have a change in routine if necessary because you never know what doors this change might open.The saying goes, "Treat others how you would like to be treated." Author Mary McAleese states that, "People with disabilities have abilities, too." We're all capable of learning and progressing towards extraordinary things and having a bit of an unforeseen defect doesn't change that. Treat a person simply for what they are, a person because "There is no greater disability in society than the inability to see a person as more" (Robert M. Hensel).
