The aim of this paper was to investigate if students can develop their understanding of English grammar through feedback by underlining. 16 students from two different classes were interviewed. They were shown an essay they had written earlier during the spring term of 2005. The teacher had underlined all errors. The students were asked to correct what the teacher had underlined and then explain what was wrong with what they had written. The results of this paper show that the students were able to correct most of the errors that had been underlined. The students in the second-year class were able to correct more errors than the first-year students could. Unfortunately, there were only six participants from the second-year class while there were ten students from the first-year class. The difference between the two classes would probably not have been as significant if there had been the same number of informants. Therefore it is difficult to draw any conclusion about how much they improved their overall understanding of English grammar. Nyckelord: Interlanguage, feedback, errors, essay writing, correction