17 U.S.C. Section 110 provides an exemption to copyright for instructors to perform or display copyrighted materials during face-to-face teaching activities. For example, it is permissible to show a full-length motion picture in class as part of the classroom learning. Note, however, that this exemption does not permit copying or distributing a work -- only displaying or performing it during class time.
To qualify for the exemption, the performance or display must be made from a legally-obtained copy. Also, the exemption only applies for courses in nonprofit educational institutions.
Also, as the title implies, this exemption applies only to in-person presentations. Diferent restrictions will apply in cases of distance learning or virtual classrooms. See Distance Learning for more information.