Using assessment results for 5th and 8th grade English language learner students in New Hampshire, Rhode Island, and Vermont, the report finds that the English language domains of reading and writing (as measured by a proficiency assessment) are significant predictors of performance on reading, writing, and mathematics assessments and that the domains of reading and writing (literacy skills) are more closely associated with performance than are the English language domains of speaking and listening (oral skills). Seven appendices are included: (1) Review of the Literature; (2) Methods of Analysis; (3) About the Data; (4) Descriptions and Reliability Estimates for New England Common Assessment Program and Assessing Comprehension and Communication in English State-to-State; (5) Confidence Intervals for Testing Differences; (6) Multilevel Modeling Procedures; and (7) New England Common Assessment Program Models. (Contains 17 notes, 1 figure, 2 boxes and 19 tables.) [For summary report, see ED504061.]