and thought it would be one that the legal beagles among us ought to keep on our radar, given the First Amendment implications.

or any other employer for that matter but especially schools.

I should have added:  Unless you own the company & have no one to answer to, sooner or later the company IT guy will see your tracks.  Depending on who finds it, you could get fired or outed...  or blackmailed...  guys have lost 6 figure jobs over the hobby.
Anyone wanting to web-porn should do no less!
H

covers that.  But unless they used the school internet access, unlikely the school IT would service the laptop mid-year.  But if this only went on line for 1 day as a test...  How was this so quickly discovered?  
There is more to this than in the article...

Your employer calls the shots with their equipment. If she did it on her own computer (not provided by the school), then you would have a first amendment issue.