Should teachers spend hours correcting students’ errors, or should they simply underline the errors, leaving it up to the students to self-correct them? The current study examines the utility of indirect feedback on learners’ written output. Journal entries from students enrolled in intact second language (L2) Korean classes (n = 40) were collected and returned to the students with all of their errors underlined (indirect feedback). The students were then given class time to either identify the target of their errors, or to self-correct them. The results were compared across two proficiency levels (beginning vs. intermediate) and across learners’ prior language exposure/learning experiences (heritage language vs. non-heritage language learners). The results showed that the learners in general were able to self-correct more than a third of their errors, and that the non-heritage language learners were significantly better at perceiving their errors on orthography and particles. It was also found that the higher proficiency and non-heritage language learners were better able to self-correct their errors on particles. The current findings suggest that simply underlining the errors and asking students to self-correct them can be helpful, especially for certain ‘treatable’ errors, including those involving orthography and particles. The findings also highlight the importance of considering individual learner factors, such as the nature and length of their prior L2-learning experience, when providing indirect written feedback.