Science Fact: Women are more likely to associate how well someone is dressed with his relationship potential; men are more likely to approach women wearing makeup.
Explanation: Everyone knows one of those guys who could have a much better love life if he would just put in a little effort, but he simply doesn't seem to care. His most versatile fashion accessory is a katana. A family of birds nests somewhere within his hair. He owns one shirt, which features three wolves howling at the moon, which is dotted with smaller wolves, who are themselves howling at other moons, ad infinitum. "Why can't I get any girls?" He wonders aloud, as a raccoon tries to tip him over because it has mistaken him for an actual garbage can.
There's a lot to worry about in high school, and we're not implying that you have to look like a J.Crew mannequin or women will mistake you for the janitor. We're especially not implying that people who come from a tough economic situation are bad and doomed to datelessness. But most people have a strong inclination to make snap judgments based on how you look, and style is especially important if you're a dude.
(The standard boilerplate disclaimer applies here: this is evolutionary psychology, which, according to some people, is worse than a million Hitlers. Think of these as neat little science facts, not hard-wired biotruths.)
The Science: In one study from the '90s, researchers measured how clothing influences hotness by asking participants to rate the attractiveness of some people pictured in various photos. The kicker was, some of the photos featured the same exact people, just dressed up in "costumes" to indicate high, medium, or low status ("costumes" meaning stuff like Expensive Suit and Fast Food Uniform, not Millionaire Dracula and Zombie Hobo). Higher-status attire made everyone appear more attractive, but women were more swayed by the person's attire than men. They also saw the higher-status guys as preferable for just about any situation, from having coffee to getting married. Now, any evolutionary psychologist will tell you this is because the women were gauging a dude's fitness as a provider, and blah blah et cetera, but you can probably also blame the fact that dudes are not very perceptive. They can't tell if your top costs $500 or is literally a potato sack with arm holes. They see a woman-shaped object and think "It a girl. Good. Kiss the face part."
What guys do notice, apparently, is makeup. They may not understand what it is they're noticing, but a 2008 study found that men approach women more often and more quickly if she's wearing makeup. The point is that noticing how guys are dressed doesn't indicate that anybody is being shallow or materialistic—or rather, that everybody is a little shallow, and we all tend to judge based on appearances; men and women just tend to do so in different ways.
So What Should I Do About It?
Whether it's fair or not, people are going to notice how well you dress (and, if you're a girl, your makeup). But dressing well means something different everywhere, and not everyone can afford the relevant fashion status symbols (monocle, cat murse, etc).
But that's okay, because status doesn't necessarily cost money—even some seemingly insignificant changes can improve the overall impression you give people. Hygiene, for example, is hugely important (if you're a dude, keep in mind that women have a better sense of smell than you, and that body spray is not a substitute for a shower). Brushing your teeth is also something women are better about, and will go a long way in making someone who is kind of gross into someone who is not so gross. If all else fails, wear red, which is a color that women associate with attractiveness, power, and sensuality, and men associate with absolutely nothing.