I am going into high school next semester. I know this will be a challenge of everything! Any good advice?
On the topic of how do you know if a girl is Christian. How bout this, ask yourself what it is to be a Christian, a follower of Christ. Once you have an answer you are satisfied with, talk to your parents about it even. Ask the girl you like what it means to her to be a Christian, if your answers are somewhat the same chances are her faith is pretty strong. But also keep praying.
High School is a rough time. Pretty much throughout highschool people made fun of me which really wore me down. But I look back and high school was great, I loved it and would do it again. So don't go into it to nervous. Just try to be an example to people. Just love people, there aren't enough people that do that. Do it even when its hard, when people make fun of you (which will happen in high school). Make sure to have a core group of Christian friends who will be able to encourage you and show you love and build you up. That is huge.