Previous research on the effects of peer-editing in bringing about language development generally examined the linguistic performance of only a few students and did not focus on specific language errors nor used a control group. To counteract these limitations, this study used a pre-test/post-test comparison group quasi-experimental design to compare the effects of peer-editing to that of self-editing on students' correction of specific language errors in revised drafts. The language errors under study are two rule-based errors (subject/verb agreement, pronoun agreement) and two non rule-based errors (wrong word choice, awkward sentence structure). Results revealed that compared to the comparison group, the experimental group significantly reduced their rule-based errors in revised drafts but not the non rule-based errors. Since both groups received teacher instruction in editing language errors, but only the experimental group engaged in peer-editing, these results may be attributed to peer-editing. The study contributes to teaching pedagogy by encouraging teachers to use peer-editing in the writing classroom and to focus on the correction of few language errors to bring about language development. (Contains 1 table.)