An interest in STEM related subjects need not be relegated to the confines of a classroom. While academics are certainly a good (and critical) way to explore these areas, it's important to seek additional means through which to gain exposure.
For starters, most high schools host a handful of after-school clubs and extracurricular activities that revolve around math and the sciences. Whether it's a robotics or coding club or students competing in a math league or science olympiad, these groups allow kids to apply their knowledge in a practical setting, learn in a relaxed environment and socialize with like-minded peers.
Internships are another great way to further investigate STEM fields. Though they're typically thought of as the domain of college students and recent graduates, it's slowly becoming more popular for high school students to pursue them as well. In fact, a number of companies even offer formal programs. For example, the American Museum of Natural History (in New York City) runs the Saltz Program where high school interns are taught to use various equipment and technologies. And, in turn, they use these new skills to help visitors investigate specimens, artifacts and even the laws of physics.
Other STEM related companies offering high school internships include NASA, Microsoft, Google and the National Institutes of Health (NIH) among many others. Programs like these are fantastic because they give students the chance to sharpen their understanding of these fields, gain insight into what a professional career entails and provide opportunities for networking.
If you're curious about STEM disciplines, do yourself a favor and explore the possibilities that exist beyond your courses.