Poor comprehension of specialised terminology presents a significant obstacle that impedes students' ability to learn science. The present study examined the influences of scientific terminology comprehension on students' cognitive processes during science-text reading. We used eye-tracking tests to examine science-text reading behaviours among 663 South Korean middle school students in the seventh through ninth grades and compared quantitative differences in eye movement between students with high and low scientific terminology comprehension levels. The results of eye-tracking tests, comprehension assessments, and a questionnaire measuring participants' familiarity with scientific terminology showed that students with low-level comprehension were less skilful at reading science texts, paid more attention to everyday words and less attention to scientific terms, and did not engage in repeated reading. Conversely, high-comprehension students engaged in longer and more repeated reading of unfamiliar terms. This study presents empirical evidence that the comprehension of scientific terminology is a primary factor influencing difficulties in science reading and learning. The findings suggest the need for teachers to assess students' comprehension of scientific terminology and devote more time to explicit teaching of such specialised vocabulary.