Welcome to the Android Forums, yooperbug!
If I read you correctly, you suspect that someone is texting you with a spoofed
phone number, correct?
Unfortunately there are lots of anonymizing web sites
that claim to be able to spoof the CallerID data. If you need to prove this, like in a court of law, you're going to need the help of a law enforcement agency to get court orders for information in at least three places.
If this is happening in the US, it's nearly certain that it crossed state lines, so you're probably at the mercy of the FBI to pick up your case, or more probably not to. Unless this is a big deal like murder, the FBI can't help you. They don't have the resources to handle "little" matters, no matter how big it is to you personally.
If you need to convince someone like a parent or school official, you can Google "Caller ID spoofing" and show them how many sites provide this service, and do it to yourself in front of them. It won't prove that your friend's phone was spoofed, but it will prove that it's really easy to do it.
Good luck! Hope that helps.