When you return papers to students, have them 1) correct any grammatical or syntactical problems you have pointed out, either on the paper itself, or on a separate sheet, and 2) respond to any marginal comments you’ve made. Perhaps offer bonus points for thorough responses. This ensures that students actually read your comments, and that they might actually learn from them. -DG
Source: Tollefson, Stephen K. Encouraging Student Writing: A Guide for Instructors. Berkeley: Office of Educational Development, University of California, Berkley, 2002. 9. http://teaching.berkeley.edu/sites/teaching.berkeley.edu/files/encouraging_0.pdf