Current composition practice relies on a decades-old summary of research concluding that a focus on grammar in students' writing is useless, or even harmful. Conversely, hundreds of recent studies from the fields of second-language writing and applied linguistics claim to provide evidence of the benefits to providing feedback on grammar in students' writing. This article summarizes the arguments for and against such feedback and problematizes the results of previous research by describing a quasi-experimental study measuring the effects, both positive and negative, of providing students with grammar feedback on their writing. Results show that, while feedback on specific grammatical forms improved participants' accuracy on those forms, it also led to decreased accuracy on other forms related to but not the focus of instruction. Furthermore, the control group's accuracy equaled or surpassed that of the two feedback groups.