Gifted girls of color represent a potentially untapped resource for increasing and sustaining a diverse science, technology, engineering, and mathematics (STEM) workforce. Girls of color possess unique mathematics and science gifts and talents that can remain unrealized if not addressed before middle school. Culturally responsive STEM out-of-school-time (OST) activities can be an effective means to develop STEM capacity in gifted girls of color. The researchers present three considerations to support the implementation of STEM OST. First, they offer a rationale for culturally relevant STEM enrichment activities for gifted girls of color. Next, the researchers consider how culturally relevant STEM OST activities can help to close the achievement gap. Finally, they explain how professional mentorship opportunities within OST activities can help gifted girls of color navigate the STEM pipeline.