This study explored the relationship between the reading ability and science achievement of students in grades 5, 8, and 9. Reading ability was assessed with four measures: word recognition, vocabulary, syntactic knowledge, and comprehension (23% of all passages were on science topics). Science achievement was assessed with state criterion-referenced measures. Both the reading and the science measures included inference items. Using multiple-group structural equation modeling, a general factor of reading ability (composed of the two specific factors of discourse comprehension and word comprehension) was found to account for 70% of the variance in grades 5 and 8 science performance and 64% of the variance in grade 9 science performance. Quantile regressions revealed that the relationship between reading and science was stable across ability levels at grade 5 and mostly stable at grade 8, with a slightly stronger relation for eighth graders at low levels of science ability. At grade 9, lower reading ability was more strongly associated with lower science performance, which was statistically significantly different from the comparatively weaker associations at higher ends. Taken together, results suggest that literacy is critical to learning and demonstrating knowledge of science concepts, regardless of ability level.