Break your classroom up into stations to look at the available sample student work from past MCAS tests. Print out short answer question answers or essays from past MCAS tests in addition to the rubrics that they were graded on. Keep what score the essay or question got hidden from students. In stations, have students look at the work, and assign what score they as a group would give the essay or short answer question according to the rubric. After students have visited the stations, go over the answers together as a class; perhaps have students show on their fingers what score they assigned before revealing the actual score. Students will have questions about why the question or essay was assigned a particular score; for the sake of time, have students pick the top two they want to review, and then read those ones out loud and have an open discussion about what students notice and observe.
Practice for ELA MCAS: http://mcas.pearsonsupport.com/student/practice-tests-ela/
Practice for Math MCAS: http://mcas.pearsonsupport.com/student/practice-tests-math/
Practice for Science MCAS: http://mcas.pearsonsupport.com/student/practice-tests-science/