Some of my students (advanced comp and grammar in Spanish) revised their papers and did not get better grades. That is because the implicit standard for a revision is a half grade higher than for the first version, so to improve they have to get a full grade higher.
On weaker papers, the issues tended to be basic vocabulary and grammar, and so I could barely deal with issues of composition proper at all.
My goal is to get all of the students to write at the upper division Spanish level, (where some of the students are starting from). A student who starts at an A level should be able to write convincingly and with elegance by the end of the semester.