One of the best ways to get better at teaching is to do it! Here are a few volunteer opportunities in the Greater Philadelphia area and beyond if you're looking to get your feet wet in education or to further your involvement in the movement to improve education in underrepresented areas:
MAST at Haverford College
Out reach Tutoring programs at Bryn Mawr College
Camp Program Intern - Academy of Natural Sciences in Philadelphia is looking for summer interns.
Informal online volunteer opportunity mentoring students and helping them develop an interest in education
In addtiion to these opportunities, do not hesitate to ask around in the Education department or in your major's department. Often, professors and administrators have additional insights into available teaching opportunities, right on campus or nearby!