Medecins Sans Frontieres/Doctors Without Borders (MSF) is one of the world's leading independent organizations for medical humanitarian aid, giving quality medical care to people caught in crisis regardless of race, religion, or political affiliation. Every day, more than 30,000 MSF field staff across 74 countries provide assistance to people whose survival is threatened by violence, neglect, or catastrophe, primarily due to armed conflict, epidemics, malnutrition, exclusion from healthcare or natural disasters.
Some positions may require specific healthcare knowledge. I would advise you (as high school students) to only to choose general medical volunteers.
Please apply at: https://www.msf-me.org/apply-volunteering