Abstract: This study reports on the measured proficiency-referenced learning outcomes during study abroad of a large, multi-institutional cohort (N=1,881) of U.S. students of Russian who have undertaken intensive language study on ACTR-administered formal language study programs at Russian universities for periods of 2, 4, and 9 months over the course of the past 15 years. The study specifically examines the effects of different durations of immersion on learning outcomes across skills, as well as potential effects of age, gender, knowledge of other foreign languages, levels of control of language structure, years of formal study, and the interaction of gains across different skills. Attention is also devoted to the role of initial (pre-program) levels of proficiency in the prediction of ultimate outcomes from study abroad terms of different durations. Results indicate that second language (L2) gain across skills is strongly correlated with longer-duration immersion programming, including systematically documented outcomes at the Superior and Distinguished Levels (ILR 3, 3+, and 4) in the case of the yearlong overseas Flagship program, now in its sixth year. The present study replicates results of an earlier ACTR/NFLC “Predictors” study (Brecht, Davidson, & Ginsberg, 1995) that structural control and pre-program reading comprehension are correlated positively with L2 gain at the semester level while demonstrating similar effects for academic year program outcomes as well. In addition, a strong correlation of pre-program listening proficiency and post-program speaking gain was noted at the advanced levels and above. By contrast, age, gender, and years of formal study were not correlated with overseas L2 gain at the advanced level and above.