The writing center tutors often see student responses that we instructors don't -- how students respond to our assignments, how students respond to our comments on their papers and our readings.  The following ideas are from the Highline Writing Tutors...

Students who see a ton of marks on a paper can feel overwhelmed. I’d suggest that teachers refrain from making an overwhelming number of marks on a student’s paper. If a student has a pattern of making the same comma error throughout his or her paper, I would suggest not marking every mistake, but rather telling them what the mistake pattern is and pointing out just a few.

I highly recommend the use of cover sheets. The comments a teacher makes on a cover sheet can cut to the point and prioritize. A rubric of some sort so students and tutors are more aware of what specific areas should be given priority and where exactly they need to focus. The best system I have seen is when teachers attach covers sheets with a guideline as to where the student’s essay strengths and weaknesses are, especially with more complex ideas such as tone and voice, cohesion, language maturity, etc. It takes the focus off of individual comments and trying to figure out what they mean, and gives me a clear guide as to how to most effectively help the student.

I have had students ask why whole paragraphs or sections have been X-ed out as there is not enough supporting commentary for the change. Teachers might use more clarification as to why the teacher wants the student to make those changes.

Even thought the comment "This is vague" points out a sentence or paragraph that is in fact vague, further descriptive guidance as to what and why something is vague would be helpful. It is sometimes difficult to understand why the teacher chose one particular part as vague as the essay may be vague in general.

I would suggest staying away from writing super-lengthy comments because they can get confusing and lose the student. If you have a lot to say or suggest to a student, it would probably be best to just write "see me." This also encourages students to talk to their instructors, something many students seem afraid to do.

Sometimes the teacher assumes what the student is trying to say, and suggests an "appropriate" replacement. In the case of ESL students, this is usually not the case, as the student knows what he or she wants to say, and has written it to the best of his or her ability. I have found that many times the student wants to express a complex idea, and does so, in the context of translating from his or her native language. When I consult with such a student, he or she will insist the change does not mean what they had intended, and it takes extensive questioning to find out exactly what they did intend. Instead of going as far as making "appropriate" revisions, I think it would be more helpful to comment on clarity.