Interesting topic.
When I was thirteen - I was dealing w/ a lot of changes. I was invited to my first ever boy/girl party. Which terrified me. Mainly because I was not really friendly w/ a lot of the people who went to the party, I was friendly w/ the girl who had the party, but she was type of girl who got along w/ anyone. Unfortunately, none of my friends went - (they were actually invited too) to the party, so I just hung around - wearing a nice outfit I bought, and I just talked to people when I felt like it.
I also started playing football, basketball, and baseball w/ a boy I started developing a crush on. Cause he took the time to show me how to play and appreciate each sport.
I remember one time specifically - I played football w/ him and his friends. I also the first girl in the neighborhood who played and excelled at all these sports. Pretty soon all the girls in the neighborhood wanted to play.
Finally - I started to realize who my friends were and who my friends were not. It took a while for me to adjust all that, but eventually I came out stronger than ever before. Since the age of thirteen - I only close friends w/ two of the friends I made during that age.
Above all - thirteen is an age that we can all learn a thing or two - we learn about first crushes, first fights, first heartbreaks, and no matter what - (at least I learned) to accept yourself who you are.