Findings are that both direct correction and simple underlining of errors are significantly superior to describing the type of error, even with underlining, for reducing long-term error. Direct correction is best for producing accurate revisions, and students prefer it because it is the fastest and easiest way for them as well as the fastest way for teachers over several drafts. However, students feel that they learn more from self- correction, and simple underlining of errors takes less teacher time on the first draft.
Chandler, Jean. “The Efficacy of Various Kinds of Error Feedback for Improvement in the Accuracy and Fluency of L2 Student Writing.” Journal of Second Language Writing 12(2003):267-96.