Question

One of your classmates talks very loudly and does not let others participate in class discussions

Answer 1

just ask that person to let others answer and answer himself only when he is recognised to.the other way is to write about his attitude in class by few students of class and sending that letter to the class teacher.
hope this helps!!!!!

Answer 2

first of all tell that person softly or politely  not to do so  and too tell him/her the importance of everyone's point of view , ask him to respect everyone's suggestions and if then also he don't listens then ignore him and never participate with him then only he/she will understand the point of class discussion and then i'll hope he/she will understand.