While fair use includes uses for teaching, scholarship, and research, you still must consider the four factors of fair use.
In particular, the effect on the potential market must be considered. For instance, copying parts of a textbook to distribute to members of a class often fails to meet the requirements of Fair Use since it affects the market of that textbook, which normally all students would have to purchase.
Use the checklist on the four factors of fair use page to weigh all four factors of fair use when deciding whether a use is infringement of copyright.