If the work has a copyright, is there an exemption for classroom or other use?
There are many exemptions for using copyrighted works under different circumstances.
One of the most common is Fair Use, which allows you to use copyrighted works in part and generally for educational or non-commercial uses.
Title 17, Section 110 of the the Copyright code eases restrictions on performance and display in classrooms and online.
Title 17, Section 121 exemptions allow for the reproduction and distribution of works for disabled people.