I'M A LITTLE late on the Valentine's Day bandwagon, due to things I'll explain later. Valentine's Day is sort of a weird midway point for high school students. It's kind of the transition time between superficial and real relationships and because of this, you see all sorts of methods to show affection on Valentine's Day.
In elementary school, everyone would bring in a class set of Valentines and the whole day would be centered around arts and crafts, songs, and just really a fun, carefree day. But all the kids were always focused on the candy in the Valentines. Of course, there would be a bit of "secret admirer" stuff every year, but like most love stories before middle school, they weren't the main focus, especially for the guys (that candy isn't going to eat itself).
In middle school, the classroom tradition was scrapped because we were "grown up," but some kids still bought Valentines and played the "you're my friend enough to get a Valentine from me" game to torture those who weren't worthy. Again, some people got things for their significant other, but it was prominent, as not every kid in middle school is in a relationship (if you can call it that).
In high school, it's more of the same - with a little more change. Kids still occasionally do the store-bought Valentines, but it's more because acting like you never left 4th grade is in style right now (that's for another post...). And since more people are in "relationships", teddy bears and chocolates are rampant across the school.
High school is the time when most relationships start to look like adult ones, so Valentine's Day starts to mirror the same trend. It's a transition time though, some kids are clinging to the past (and their cartoons Valentines), while others are welcoming their future of actually taking their girlfriends out for dates.