I used to wear it until I lost it.
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For all you asking what is a school ring: in the US you can get a ring with your high school name and mascot logo on it and the year you graduate. Usually with the birthstone in it. I don't know if other countries do this or just the US. The ring is customizable; if you are in a sport you can get that info placed on it also. Usuaully people will have their initials or name engraved on the inside of the band.
They are not free have to buy it. People in college will sometimes get class rings too, especially if you are in a fraternity or sorority.
Further info; it used to be a custom that a guy would let his girlfriend have his ring when they were dating. Of course she was supposed to return it to him if they broke up. The girl would wear the ring on a necklace to show she was dating someone. OR if the ring was not too large try to wear it on her finger. It is kind of old fashioned custom now. I don't thing this is done much these days. It was still done a little when I was in school but it is a much older custom like back in the 50's - 70's.
Here is a link to a seller so you see what they look like:
http://www.jostens.com/rings/highschool/index.asp
http://www.joyjewelers.com/modules/classrings/
wikipedia link for further info
http://en.wikipedia.org/wiki/Class_ring