This study examined the contributions of vocabulary and spelling to the reading comprehension of students in grades 6-10 who were and were not classified as English language learners. Results indicate that vocabulary accounted for greater between-grade differences and unique variance (?R[superscript 2] = 0.11-0.31) in comprehension as compared to spelling (?R[superscript 2] = 0.01-0.09). However, the contribution of spelling to comprehension was higher in the upper grade levels included in this cross-sectional analysis and functioned as a mediator of the impact of vocabulary knowledge at all levels. The direct effect of vocabulary was strong but lower in magnitude at each successive grade level from 0.58 in grade 6 to 0.41 in grade 10 while the indirect effect through spelling increased in magnitude at each successive grade level from 0.09 in grade 6 to 0.16 in grade 10. There were no significant differences between the language groups in the magnitude of the indirect impact, suggesting both groups of students relied more on both sources of lexical information in higher grades as compared to students in lower grades.