diff --git a/mod/assign/module.js b/mod/assign/module.js
index a1618b76fe8..4f9f8c03f17 100644
--- a/mod/assign/module.js
+++ b/mod/assign/module.js
@@ -23,17 +23,21 @@ M.mod_assign.init_grading_table = function(Y) {
             node.on('change', function(e) {
                 rowelement = e.currentTarget.get('parentNode').get('parentNode');
                 if (e.currentTarget.get('checked')) {
-                    rowelement.setAttribute('class', 'selectedrow');
+                    rowelement.removeClass('unselectedrow');
+                    rowelement.addClass('selectedrow');
                 } else {
-                    rowelement.setAttribute('class', 'unselectedrow');
+                    rowelement.removeClass('selectedrow');
+                    rowelement.addClass('unselectedrow');
                 }
             });
 
             rowelement = node.get('parentNode').get('parentNode');
             if (node.get('checked')) {
-                rowelement.setAttribute('class', 'selectedrow');
+                rowelement.removeClass('unselectedrow');
+                rowelement.addClass('selectedrow');
             } else {
-                rowelement.setAttribute('class', 'unselectedrow');
+                rowelement.removeClass('selectedrow');
+                rowelement.addClass('unselectedrow');
             }
         });
 
@@ -45,14 +49,16 @@ M.mod_assign.init_grading_table = function(Y) {
                     checkboxes.each(function(node) {
                         rowelement = node.get('parentNode').get('parentNode');
                         node.set('checked', true);
-                        rowelement.setAttribute('class', 'selectedrow');
+                        rowelement.removeClass('unselectedrow');
+                        rowelement.addClass('selectedrow');
                     });
                 } else {
                     checkboxes = Y.all('td.c0 input');
                     checkboxes.each(function(node) {
                         rowelement = node.get('parentNode').get('parentNode');
                         node.set('checked', false);
-                        rowelement.setAttribute('class', 'unselectedrow');
+                        rowelement.removeClass('selectedrow');
+                        rowelement.addClass('unselectedrow');
                     });
                 }
             });