Middle school, early high school transition:
Skater-look (even though I was really a biker): long baggy shorts (or jeans) hanging way too far away from my natural waist, chain hanging from pocket of shorts holding onto my wallet, baggy tees with writing on them (not "˜obscene', btw), lots of stuff from Alien Workshop.
Later in high school:
Lots of Polo / Tommy Hilfiger polo shirts, better fitting tees, lots of jeans / cotton pants. Still intermixing with baggy shorts. I slowly, SLOWLY started to purchase stuff at Brook Brothers; first polo shirts and then more "˜adult' items.
After high school, before college (I took a sabbatical to work in the family business and to get a kick at real life):
Lots of Zegna / Brooks Brothers shirts, wool or cotton pants, more and more v-neck sweaters and sweater vests; suits / sport coats if needed.
Of course, I'm wearing a combination of the different trends, depending on occasion and how much people around me (or myself) will probably drink.