Who Owns Teacher's Lesson Plans

Recently, Teachers Paying Teachers reported that a kindergarten teacher earned $700,000 from selling her lesson plans through their website.  But the NEA reports that school districts own lesson plans if they are created within the scope of the duties and responsibilities of a teacher.  http://www.nea.org/home/37583.htm. Who is right?  It appears that the NEA is right and some school districts have successfully sued teachers to recover the profits the teachers have made selling lesson plans.  Teacher Pay Teachers covers its potential liability by requiring selling teachers to represent that they own the lesson plans. If the teachers do not own the lesson plans, then Teachers Paying Teachers can sue the teacher to recover its damages for copyright infringement.  Teachers have asserted that they created the lesson plans on their own time using their own resources and, therefore, own the lesson plans.  The problem with that argument is that it fails under the US Copyright Act. Since teachers are salaried, they are on the clock 24/7.  If they used their resources, it does not change the fact that they created the lesson plans as part of their duties as an employee/teacher.

This issue is really the same song, second verse of the ministers and ownership of sermons.  If the sermon or lesson plan is created as part of the job duties, the employer owns it.  If the employer wants to transfer ownership to the employee via a written contract, then the employee must pay at least fair market value for the intellectual property or it could cost the employer it's tax exempt status.