This project involves the collaboration of researchers with 24 teachers in a study aimed at investigating and improving the vocabulary knowledge and reading comprehension of 4th and 5th grade students for whom English is a second language. Cross sectional and longitudinal data were collected on various aspects of vocabulary knowledge, vocabulary inferencing, and reading comprehension of English language learners (ELLs) and English-only peers. Researchers and teachers collaborated in developing and implementing intervention strategies directed at improving vocabulary knowledge and reading comprehension in the ELLs. In the first year of the study, the vocabulary knowledge of ELLs and English-only students were examined. In the second year of the study, the intervention (exercises aimed at improving vocabulary knowledge) was implemented at sites in Virginia, Massachusetts, and California. In the third year of the program the intervention was again administered to the same children, now fifth graders and to some other fifth graders who had not been in the study the previous year. Case study analysis of individual students indicated that students who were in the intervention were more likely to employ strategies they were taught to infer meanings than were the control students. It is concluded that the intervention was successful in improving vocabulary development. (Contains 26 references.) (KFT)