Many academics wish to assign their own previously published work to students for class reading. This is generally fine if the library licenses the particular journal that the Professor wishes to assign as reading to students--in which case, the best practice would be to link to the material directly from the University Library.
But, what if the University does not license to use that particular journal? Then the Professor must consider his/her own individual copyright agreement with that particular journal. Does the copyright agreement permit for classroom distribution of the article? Note: the contract with the publisher trumps general copyright law defenses, such as fair use.
In order to proactively protect work in the future, Professors should think about potential uses they may wish to make of their own work (such as public presentations at conferences, placing a copy of the journal article in the University's Institutional Repository–IDEALS, or classroom teaching purposes) and include an exception or reserve the right to use the work for that purpose in the copyright agreement.
One potential source of information for future copyright negotiations is the SPARC Author's Addendum, which is a ready-made addendum to any publishing agreement reserving academic uses to the author.