Glossing has been shown to have favorable effects on incidental vocabulary acquisition in second language learners. Expanding upon this line of research, we explored whether the effects of glossing may vary as a function of learner proficiency. To this end, Korean eighth graders (N = 104) were instructed to read a short story (1,002 words) for meaning. The story included 18 glossed target words that occurred 1, 3, or 5 times. They then responded to a reading comprehension test, followed by a battery of unannounced vocabulary tests (form recall, meaning recall, meaning inference) immediately and one week after reading the story. Overall, the high proficiency (HP) learners tended to outperform their low proficiency (LP) counterparts in all measures of lexical knowledge. Interestingly, the magnitude of difference between the two groups as measured by Cohen’s d was most pronounced in meaning inference, followed by meaning recall and form recall. Taken together, our findings indicate that glossing may widen the gap between the HP and LP learners, rather than closing the difference between the two proficiency groups.