Rubrics
The links I have here will take you to two sites. The first site, authored by the University of Texas at Austin, gives a thorough overview of the benefits and types of rubrics. If you have the patience to read all of the information, it explains how assignment-specific rubrics eliminate guesswork for students and help instructors pare down their grading responsibility. The most important part of this site (and others) is the emphasis on having students participate in creating a rubric. Yes, devote one class meeting—treat it as a brainstorm session or something more formal, if you wish—to discussing and reaching a consensus on the measurement method by which you will assess students' performance and knowledge. The students walk away with a more thorough understanding of the assignment, their role in meeting the assignment expectations, and—perhaps most importantly—their direct participation with their own learning. Developing Grading Rubrics
Of all the rubrics I researched, this next link seemed to represent the best cross-disciplinary approach to responding to student writing. Feel free to download it and make adjustments as you deem necessary. Example of a Grading Rubric For a Term Paper in Any Discipline