If your high school student has always wanted to learn more about art, encourage them to learn how to sketch over winter break. You may even be able to find local winter break programs for high school students that can teach them this skill or enroll in an online art class.
While they may not be able to become a photorealistic artist in just a few weeks, they likely will be able to master the basic principles of art such as shading, texture, shaping, and color theory, and they may have the foundation to take their art to the next level.
If your student wants to learn more about art, you can use materials you have around the house, but buying some basic sketch pads and pencils can go a long way to help them feel more like a real artist.