When the student has the assistance of an interpreter, direct the conversation to the student who is deaf since the communication is with that student rather than the interpreter.  Slides and videotapes reinforce what is being said.  However, these materials may be difficult to interpret due to sound quality and speed of delivery.  Provide a written script to the interpreter and student in advance if it is available.  Notices of class cancellations, assignments, etc. can be put in writing or on the board to ensure understanding.