During the middle school years, interest in Science Technology Engineering and Math (STEM) falls off, especially among Black and Latinx students and women. In underserved districts, a small percentage of students graduate prepared for college and even less are prepared for undergraduate STEM coursework. Beginning in the 2009-10 academic year, we implemented an informal STEM program for upper elementary and middle school students from a nearby underserved district. Students chose from STEM offerings including hands-on engineering and computer technology courses, coding courses, and physics courses taught through hands-on activities and video games. We found that participants are similar in ethnicity, poverty, and residency, but outperform non-participants in a variety of New York State standardized measures of achievement while participating in the program and years after leaving. For example, program participants outperform non-participants in high school assessments in physics, chemistry, and math. They are also over-represented in advanced science classes, and in receiving diplomas with advanced designation - a key indicator of preparedness to pursue a STEM major in college.