Copyright law is very supportive of performances or displays of copyrighted works "by instructors or pupils in the course of face-to-face teaching activities of a nonprofit educational institution, in a classroom or similar place devoted to instruction, unless, in the case of a motion picture or other audiovisual work, the performance, or the display of individual images, is given by means of a copy that was not lawfully made under this title, and that the person responsible for the performance knew or had reason to believe was not lawfully made." Section 110(1)
This means that any type and any amount of a copyrighted work can be displayed in the traditional class setting (images, text, other static works) and/or performed in that class setting (such as an entire movie), with the only caveat being that the movie/audiovisual work must have been lawfully made, i.e., not a bootleg or pirated copy. Note that the requirement is "lawfully made." A 'fair use' copy of a work is lawfully made. A purchased, loaned or rented copy is lawfully made and qualifies under this provision unless the owner of the physical copy has entered into a specific agreement that governs how and where the work can be used. Note also that under this provision the showing (performance) of a work must be for educational purposes, not, for example, entertainment.
Section 110(1) thus enables students to watch movies, live experiments, hear lectures, view materials and listen to music. They left the classroom with new ideas, facts, memories, and their notes. All lawful uses not requiring permission of the copyright holder. Why so easy? Because it is nonprofit educational use. Because there is no lost market. No copies are being made, except for perhaps a single overhead slide or projector copy (fair use); students have no copies of the works seen or heard and the law recognizes that such public performances and displays, under these specific circumstances, are so beneficial as to outweigh any harm to a market for the works used.
A teacher or student DO NOT need copyright permission
In a physical classroom to perform (movie, AV, music, plays)
For an educational purpose to display (show photo, image, text, etc.)
At a nonprofit educational ANY work
institution ALL of the work (no pirated copies)