What experience can students gain while still in high school?
My own kids found that volunteering was a very positive way of gaining experience in working with other people and as part of a team. Volunteering also is a very good way of building a solid resume that colleges like to see.
All the best,
Based on my experience, some ways that my young adults and immediate family members gained experience and development was by "volunteering". For example - my niece volunteered to teach dance lessons at her studio and eventually started charging a fee due to high demand. When she got to college she was able to maintain her dance lessons and picked up teaching dancing on the side. This worked out well for her because she enjoys dancing and got paid doing it.
Another way to gain experience and development is to "shadow" others in areas you are interested in. Seek out individuals that may not mind helping you out. Let your network know that you are seeking to gain experience and development. They may be open to taking you under their wings for mentorship.
I wish you much success and the best of luck!