Well wouldn't this assume the teacher was on the clock or at work creating these lesson plans? When I worked at IBM I wrote a database system and I did it on my own time at home and let them use it. When I left I took it with me and my boss said hey that is intellectual property. I told him I did not write this at work I wrote it at night at my house therefore it is my property. Most teachers I know work on lesson plans during the summer at home. In most cases I'm sure they could claim to have and put the burden of proof on the school.