This study examined how Korean EFL learners’ judgments of the grammatical acceptability of non-canonical because + X constructions change, using a usage-based grammar framework. It tested the hypothesis that acceptability judgments are not fixed by traditional rule-based knowledge but can shift through repeated exposure to authentic usage in different discourse contexts (academic/curriculum versus SNS/everyday). The study involved 58 learners, evenly divided into an experimental group (n = 29), which received exposure materials, and a control group (n = 29). Pretest results showed no significant differences between the groups, indicating that learners initially viewed because + X constructions as ungrammatical. However, posttest results indicated a significant difference, with the experimental group giving higher acceptability ratings. These findings suggest that repeated exposure to authentic usage examples changed the experimental participants’ perceptions of grammatical acceptability, leading them to recognize the non-canonical because + X construction as grammatically valid. The results offer valuable insights for developing English curricula and instructional materials in educational settings.