I get asked a lot about exactly what PII is and how does it tie into FERPA.  FERPA or the Family Education Rights and Protections Act was designed to offer more protection to students in the digital world.  Part of this act included restrictions and limitations regarding distribution of personal data (PII).  A full list of PII can be seen below.
At the end of the day, it is the school's responsibility to protect this information from the public at large (not just strictly digital entities).  The two most common breaches of this act occur when a teacher encourages a class to sign up for a free online service (which require a first and last name, the very first restricted data point) or when a staff member retires and takes a copy of their digital work home for use after retirement that contains student assignments.  These are not the only cases but the most frequent.
Please keep this in mind when you are emailing people outside of our organization, working with your class on digital projects or simply taking work home to grade it.  We as an educational nation are struggling to adjust to the new requirements as they require a change of view and practice.  Please just keep them in mind as we move forward.