In this longitudinal study, the cross-language transfer from second language (L2) to first language (L1) was examined among Spanish-speaking English-language learners in an English intervention (Grades 1-3) in the southwest United States. Path analysis revealed statistically significant transfers (ps < 0.05) for the treatment group from English reading comprehension to Spanish reading comprehension. English vocabulary and English grammar also had an indirect influence on Spanish reading comprehension through English reading comprehension. For the comparison group, no English to Spanish paths were statistically significant. We concluded that intervention activities in L2 influenced L1 reading even when L1 instructional time was reduced.