This study set out to determine how students perceive writing quality in the presence of specific errors. Error pattern was a within-subjects variable with four levels: no errors, superficial (mechanical) errors, substantive (conceptual) errors, and both types of errors. All participants assessed a randomized selection of four essays containing each of the four error patterns. Overall ratings of writing quality decreased with the presence of errors; superficial errors had a significantly larger impact than substantive errors. In addition, participants rated traits about the author of the essays lower with the presence of errors in a similar pattern to writing quality.