I taught at a Philadelphia-based non-profit called Minds Matter from 2016- 2018 weekly as a Sophomore Math Instructor. We focused on helping students from low-income families gain college admissions. Teaching standardized test can be fun as long as you come up with the most exotic examples once in a while.
Here are some science-y workshops I like and ran over the years:
DNA Extraction Workshop for Penn NanoDay. It gets messy sometime, but it's always a lot of fun (plus it encourages everyone to eat more strawberries). It can be done easily with simple household materials.
Sunscreen Workshop for GEARS (Girls in Engineering And Related Sciences) Day. You can find related resource here.
Silly Putty Workshop for Girl Scouts' Day at Rice University. Soft Matter and polymer science at work! You can find this workshop along with other Girl Scouts' Day resources here.
As an undergraduate, I partnered with PAIR Houston (Partnership for the Advancement & Immersion of Refugees) to help newcomers build English skills and with their social, emotional needs as they come here to start their new life.
My other pro bono work includes a weeklong service trip to Camp Courageous at Monticello, IA to work with individuals with special needs as part of an Alternative Spring Break trip in the spring of 2015.
Earlier in college, I completed a 4-month internship at City of Houston Volunteer Initiative Program. My job assignments included securing housing for Americorp volunteers and conducting a social study on volunteering behavior and hypothesis.