ORIGINAL: RodgerPM
I'm not big promoter of AMA and I started without it but the insurance you have if you fly at an AMA field can save you if you hit something or worse yet someone.
You do not have to fly at an AMA field to be covered under AMA insurance and it is a very cheap price to pay compared to what you could be liable for if you do have an accident. For people under 19 it is only $1 per year, it is a no brainer.
Here is a copy of the AMA membership manual:
http://www.modelaircraft.org/PDF-files/Memanual.PDF