UX Design is shorthand for User Experience Design and high school students should learn how it is different from creating art.
Everything we use in our lives was designed by someone but most people aren't aware of the many decisions that were made on their behalf when a product or service was designed. UX designers make things that work for people other than themselves.
One way to get students started in understanding UX design is to have them find examples of designs that don't work. Interacting with a product or service should feel like a good relationship and should demonstrate that the designer cares about you and not just how cool their design is. Before they design anything, UX designers learn about the people who will use it or it will be like trying to do something nice for someone you don't know. People like and need different things so it's important to find out what they want.
The person who will use the design is not you, so don't design for yourself. Find out what the user really wants or needs. This is called user research.
Click on the heading above to see a cute video talking about what a UX Designer does that your students might like to see.