You need to clear this with your school to see if you can do this. Just because you want to doesn't mean they will allow it. There are some folks that are allergic to pets with fur, so you need to find out what their policy is. Then ask the teacher if they think this is a good idea. My cats would never allow themselves to be leashed so hopefully you've leashed your cat before. If not, putting a cat on a leash will be ugly, so be prepared.
I am doing a speech for class about Animal Therapy. The professor said is should be memorable. Should I bring my cat who has helped me cope with mental illness to class and have him sit on a leash while I do my speech?
Unless your cat is both used to being on a leash AND in strange environment around a lot of people, it may cause a lot of stress to your cat. Most cats wouldn't tolerate that kind of setting well.