Science education as a part of STEM education is becoming important not only for the future success of the individual but also for the economic development of the nation. This study explores the global pattern of extended education and its impact on learning outcomes in the area of science. First, the study found substantial national differences in access to afterschool science programs. Children and youth in developing countries generally lack opportunities to learn science after school, which was found to predict PISA 2015 science achievement in this study. The study suggests that inequality in extended education among countries requires urgent attention, as does inequality within countries. Second, the study found a negative relationship between additional study time for science and PISA science performance at the national level. Regarding this finding, it is speculated that the content of learning during additional study time differs from that of higher-order learning experiences measured by the PISA science test. The result may also be explained by the argument that the purpose of additional afterschool study is usually remedial lessons and/or test preparation. This cross-national research will provide insights to policy makers who intend to find global patterns in extended education, develop policy direction at the global level, and offer advice to national governments.