How many times may I use copyrighted materials covered by the TEACH Act before I have to request permission from the copyright owner? (copyright.psu.edu)
"The TEACH Act is not an application of fair use with its restrictions on any continued reuse of the same materials. Instead, it is a version of the exemption for public performance in the classroom rules. Just as the public performance exemption does not require that a professor (or institution) destroy the slides made for presentation in class (or copies of movies or other content made for display in class), the TEACH Act also does not require such an action."
SUMMARY: "...if the uses are TEACH Act qualifying uses (meeting those restrictions specified within the TEACH Act text) then no authorization or royalties are necessary regardless of the number of times the materials are reused or the span between such uses.
If the material is “fair use” dependent, then reuse by the same instructor in the same or a similar course would likely trigger a need for authorization and royalties."