In this chapter, the authors report on how inner city high school students learn science through participation in an after-school science program called Explore! Project-based science instruction (PBSI) was used as the main method of instruction in which students had the opportunity to plan, implement, and present their own scientific investigations of urban ecosystems in Queens, New York City. The authors are convinced that with proper funding and support, project-based after-school science programs such as the one described in this chapter could bridge the science achievement gap, particularly among underrepresented groups.