In this meta-analysis, I have reviewed published and unpublished research on single-track, year-round education's effect on science and social studies achievement, 2001-2016. Of 30 studies that met inclusion criteria and had data from which an effect size estimate could be calculated, 7 reported science outcomes (18 effect size estimates) or social studies outcomes (9 effect size estimates). All estimates were from Grades 3-8 in the United States. The mean magnitude of the effects (using Cohen's "d") were +0.11* in science and +0.13[superscript +] in social studies, showing an average gain of about 1 month of learning in each subject area. The estimates for mean achievement are large enough to be policy relevant, align with recent meta-analytic estimates for reading and math effects from year-round education, and are also approximately the same magnitude as measured decreases in achievement caused by summer learning loss.