The Americans with Disabilities Act (ADA) was enacted to ensure those who cannot use media (text, audio, and other methods of communicating) have access to the information they need in a format they need. (Of course there are many aspects of life affected by the ADA, but this post focuses on digital media.) Teachers are among the public employees who have an obligation to ensure they materials they use in classrooms are ADA-compliant so they can be used my all.
Exactly what one should do to be ensure works are ADA-compliant can be confusing, especially for those teachers who do not encounter students with this need on a frequent basis. This is further complicated by the kluge of materials that a teacher typically uses—instructional materials come from many publishers (including the teacher) and some are reused (with or without modification) year after year.
Many teachers pay little or no attention to the need to make materials ADA compliant, and they can reasonably argue that it is a low priority if there are no students actively using the features of files that make them compliant. In many cases, the features that make files ADA compliant make them better and more effective teaching materials, so the time needed to ensure files are accessible both supports all learners and ensures quick access if a student arrives who needs the features.
The easiest way teachers can begin to develop a collection of ADA-compliant materials is to use the accessibility checker which is built into Microsoft Office. Run the checker to see a list of errors (things that must be changed) and warnings (things that should be changed) to make the files accessible.