This document discusses mistakes and feedback in English language teaching. It defines mistakes as performance errors that can be self-corrected, while errors are systematic deviations that cannot be self-corrected. It categorizes mistakes into slips, errors, and attempts. The causes of errors include L1 interference, developmental errors, and overgeneralization. The document also discusses assessing student performance through tests, comments, marks, reports, and self-assessment. It explains that feedback should be given on oral and written work, and outlines principles for giving effective feedback such as focusing on behaviors that can change and suggesting alternative behaviors.