These are the things that schools make people's parents sign before a student goes on a field trip. Apparently, they have absolutly no legal standing but they are still quite popular anyway. The idea is that if your child is accidentally killed or maimed, the school isn't held responsible.
That said, here is the exact text of the important part of an "Extended Field Trip - National/International Travel Parental/Guardian Authorization Form" that my cross-country team has to return for a 180 mile bus trip from Minneapolis to Duluth (parenthesis are mine and yes, there are a lot of big words):
"The undersigned parent or guardian, of behalf of ______________________ in consideration of participation by the student in said field trip, herewith assumes all risks of said trip, and agrees to hold harmless Special School District #1 (Minneapolis Public Schools) for all damages from injury to a person or property arising out of any act not under the control of said School District, including but not limited to the following (here's the good part): insurrection, revolution, air piracy, abduction, kidnapping, any act of aggression by a foriegn government or its citizens, civil war of rebellion, and any act whether accidental or otherwise perpetuated (sic.) by anyone not under the direct control of said School District."