I would guess the "other adults" to be teachers, guidance counselors, the principal...or any other adult who will listen.
My neice used to cut herself during a very bad time in her life in her early/mid teens. I also have an ex boyfriend who was doing it 20 years ago. From what both said to me, Ebbie is mostly right. It was done to prove they still had feelings but also to mask other feelings (like stubbing your toes to forget about your toothache, simply put) and there are some people who even say it is a stress relief for them, like their anxieties flow away with the blood or the act of cutting. I'm by no means an expert but I know it's been around for awhile now.