The current meta-analysis study summarizes the effects of the GlobalEd Project, a web-based educational intervention of international negotiations embedded within social studies curricula, on middle and high school students' interest in social studies and negotiation self efficacy. Meta-analytic evidence supports statistically significant increases in students' interest in social studies for both middle and high school students and negotiation self-efficacy for high school students only as a result of participating in GlobalEd. Results demonstrated different effects of the intervention on middle and high school students, indicating greater increases for high school students. Significant effects of moderators related to demographic composition of samples were found for both interest in social studies and negotiation self-efficacy. Finally, after controlling for effects of school, proportion of those students who intend to go to college and who watch national news were contributing to the increase of interest in social studies. (Contains 3 footnotes, 3 tables, and 2 figures.)