Going to class is a big part of being a classical musician. But have you heard of a "master class"? You perform a piece in front of a class and then the "master" leading the class critiques it. Sounds nerve-wracking (read: like the stuff of nightmares) to us. In this special assembly with Classroom's first substitute teacher, Maggie Molloy talks to Itzhak Perlman about the master class, and how his new addition to the MasterClass online series makes it possible to take a class from him.