groupId: function(group, prefix) {
                        return (prefix || "") + "group" + group;
                },
-               togglePresence: function(s) {
-                       s.present = !s.present;
+               togglePresence: function(student) {
+                       const sIdx = this.students.findIndex( s => { return s.number == student.number; });
+                       Vue.set( this.students, sIdx, Object.assign({},student,{present:!student.present}) );
+                       //s.present = !s.present;
                },
                allFinished: function() {
                        for (s of this.students)
                        {
                                if (!s.present)
                                        continue;
-                               const paperIdx = this.assessment.papers.findIndex( item => { return item.number == number; });
+                               const paperIdx = this.assessment.papers.findIndex( item => { return item.number == s.number; });
                                if (paperIdx === -1)
                                        return false;
                                const paper = this.assessment.papers[paperIdx];
 
 /*table { border: none; border-collapse: collapse; }*/
 table.in-question td { border-left: 1px solid grey; }
 table.in-question td:first-child { border-left: none; }
+
+.absent {
+       opacity: 0.5;
+       background-color: lightgrey;
+}
 
                                                                        th Name
                                                                        th(v-for="(q,i) in assessment.questions") Q.{{ (i+1) }}
                                                        tbody
-                                                               tr.assessment(v-for="s in studentList(group)")
+                                                               tr.assessment(v-for="s in studentList(group)" :class="{absent:!s.present}")
                                                                        td(:class="{blur:!!s.blur,resize:!!s.resize,disconnect:!!s.disco}" @click="togglePresence(s)") {{ s.name }}
                                                                        td(v-for="(q,i) in assessment.questions" :style="{backgroundColor: getColor(s.number,i)}" @click="seeDetails(s.number,i)")  
                                        h4.title(@click="toggleDisplay('assessment')") Assessment