Join science outreach groups. For example, BOOST works with Durham Public School students in grades 5-12, and STEM in the Park facilitates sustained, hands-on mentoring and engagement opportunities for underrepresented minorities, girls, and students from low-income backgrounds in grades 5-12. WiSE (Women in Science and Engineering) runs an active listserv with many science outreach opportunities for both women and men, as does the Office of Postdoctoral Services (yes, grad students can subscribe!).