The international "FIRST® LEGO® League (FLL): Challenge" is a popular educational robotics and STEM competition designed to promote primary and early high school students' STEM interests and careers, and twenty-first century skill development. The "FLL Challenge" currently involves over 318,000 students (aged 9-16 years) in approximately 110 countries. In this paper, we present a semi-systematic historical review of the research literature focussed on the competition's impact on school students' STEM attitudes, learning, and twenty-first century skill development. Through our review process, we found a total of 26 publications between 2004 and 2022 which met our inclusion criteria, and identified the emergence and development of three significant historical research themes: (1) impacts on students' motivation, STEM learning, and attitudes, (2) development of twenty-first century skills, and (3) coaching/pedagogical strategies to support student learning and skill development. The first theme was further refined through three subcategories focussed on impacts on female participants, ethnic minority groups, and students with special needs. International research findings regarding the impacts of "FLL Challenge" participation on students' motivation, STEM attitudes, and learning were positive for all student groups, especially female participants, but not always statistically significant. Findings regarding positive short-term impacts on twenty-first century skill development were broadly consistent, but long-term impact findings were inconclusive. The influence of coaches' skills and pedagogical expertise upon students' learning and skill development in the "FLL Challenge" is a potentially underrepresented area of research.