This meta-analysis explores the impact of informal science education experiences (such as after-school programs, enrichment activities, etc.) on students' attitudes towards, and interest in, STEM disciplines (Science, Technology, Engineering, and Mathematics). The research addresses two primary questions: (1) What is the overall effect size of informal science learning experiences on students' attitudes towards and interest in STEM? (2) How do various moderating factors (e.g., types of informal learning experience, student grade level, academic subjects, etc.) impact student attitudes and interests in STEM? The studies included in this analysis were conducted within the United States in K-12 educational settings, over a span of thirty years (1992-2022). The findings indicate a positive association between informal science education programs and student interest in STEM. Moreover, the variability in these effects is contingent upon several moderating factors, including the nature of the informal science program, student grade level, STEM subjects, publication type, and publication year. Summarized effects of informal science education on STEM interest are delineated, and the implications for research, pedagogy, and practice are discussed.