K-12 schools play a pivotal role in fostering science, technology, engineering, and math (STEM) literacy. STEM classes can help students hone the analytic and problem-solving prowess they need to face complex challenges at home, at work, and in the world. STEM skills and knowledge can prepare students to pursue a wide range of rewarding careers. Over a lifetime, a solid STEM education can ensure that people crack the code of complex STEM issues in headlines and on ballots and make wise decisions. Yet while all students need a strong STEM education, far too many students graduate from high school without a solid foundation of STEM skills and knowledge. This is especially true for youth of color, youth from low-income communities, youth with disabilities, youth who are English learners, and young women--all of whom are underrepresented in the STEM workforce. This brief explores factors that contribute to opportunity gaps in STEM education based on race, ethnicity, gender, ability, and socioeconomic status. It showcases the work of several the National Science Foundation's Discovery Research PreK-12 (DRK-12) projects and describes promising approaches for removing barriers for underrepresented groups and enhancing the STEM learning of all students.