I've decided that I'm going to report a group of girls in my class for being excluding me and others.
That's quite a decision to make. How are they excluding you and the others?
They're not letting us join in on a group project.
It makes sense that you're going to let someone know how they're excluding you. Learning that that kind of behavior is wrong and hurtful is part of the education process.
I'm going to tell the teacher what they're doing.
I'm sure the teacher will agree that what they're doing isn't appropriate behavior. Hopefully they'll learn their lesson.