The authors investigated the mediating effects of general academic and science-specific vocabulary on science reading comprehension among English learners (ELs) of varied proficiency. The sample included 169 regular education Grade 7 students (86 current ELs; 83 former ELs) enrolled in 1 urban school in Pacific Northwest region of the United States. The results indicated that both vocabulary types--rarely explicitly taught at the secondary level--were significant contributors to reading comprehension, above and beyond EL status. The full parallel mediation model accounted for 55% of the variance in science reading comprehension. Notably, the mediating effects of both vocabulary types were significant and statistically similar in size, yet, not sufficient to fully explain ELs' reading scores. Implications and directions for future research are discussed.