Effects of Spanish immersion on children's native English vocabulary were studied. Matched on grade, sex, and verbal scores on a 4th-grade Cognitive Abilities Test (CAT), 30 5th- and 6th-grade immersion students and 30 English monolinguals did 60 consecutive Peabody Picture Vocabulary Test (PPVT) items. They also did a 20-item Spanish-English Cognate Test (SECT), similar to PPVT, on recognizing low-frequency English words with high-frequency Spanish cognates. The CAT and conventionally scored PPVT revealed comparable verbal ability between groups, but on 60 consecutive PPVT items, immersion did better than control (p = .002) because of cognates. On SECT, immersion significantly outperformed control (p <.001; effect sizes: 5th grade = 1.72, 6th grade = 1.45). Findings support the idea that Spanish immersion has English-language benefits and that positive transfer (crosslinguistic influence) occurs from Spanish as a foreign language to native English receptive vocabulary.