Strangely enough, I do get a fair amount of questions from acquaintances currently in the realm of academia about what constitutes Fair Use. It is interesting to note that Fair Use as we know it does not generally have a direct parallel in other English-speaking countries. The UK has Fair Dealings, which is much stricter and has much less wiggle room for interpretation, especially for use in the classroom.
So, I give you this. The official wording of the Fair Use clause as stated in section 107 of the Copyright Act.
The four clauses of Fair Use are as follows:
1. The purpose and the character of the use, including whether it is for commercial or non-profit educational purposes
2. The nature or type of the copyrighted material (i.e., periodical, film, book, etc.)
3. The amount and substantiality of the portion used in relation to the whole
4. The effect of the use on the potential market for or value of the copy-righted material
The third one in particular is difficult for interpretation. What if I were to copy a whole book for my class? That would be copyright infringement not covered by Fair Use. Copy the first six pages of every chapter? That might be considered Fair Use, as long as it is in a classroom setting.