diff --git a/grade/lib.php b/grade/lib.php
index e241c7ae9879c..007921ec0858b 100644
--- a/grade/lib.php
+++ b/grade/lib.php
@@ -2489,11 +2489,12 @@ public function get_cell_action_menu(array $element, string $mode, grade_plugin_
                     }
 
                     if (($element['type'] == 'userfield') && ($element['name'] == 'fullname')) {
-                        $sortlink->param('sortitemid', 'firstname');
+                        $usernamefields = core_user::get_user_full_name_fields();
+                        $sortlink->param('sortitemid', reset($usernamefields));
                         $context->ascendingfirstnameurl = $this->get_sorting_link($sortlink, $gpr);
                         $context->descendingfirstnameurl = $this->get_sorting_link($sortlink, $gpr, 'desc');
 
-                        $sortlink->param('sortitemid', 'lastname');
+                        $sortlink->param('sortitemid', end($usernamefields));
                         $context->ascendinglastnameurl = $this->get_sorting_link($sortlink, $gpr);
                         $context->descendinglastnameurl = $this->get_sorting_link($sortlink, $gpr, 'desc');
                     } else {
diff --git a/grade/report/grader/lib.php b/grade/report/grader/lib.php
index c0b1a5b7bd57f..5738bee56ca5e 100644
--- a/grade/report/grader/lib.php
+++ b/grade/report/grader/lib.php
@@ -356,6 +356,7 @@ private function setup_sortitemid(string $sort = '') {
             $SESSION->gradeuserreport = new stdClass();
         }
 
+        $namefields = core_user::get_user_full_name_fields();
         if ($this->sortitemid) {
             if (!isset($SESSION->gradeuserreport->sort)) {
                 $this->sortorder = $SESSION->gradeuserreport->sort = 'ASC';
@@ -378,10 +379,10 @@ private function setup_sortitemid(string $sort = '') {
         } else {
             // not requesting sort, use last setting (for paging)
 
-            if (isset($SESSION->gradeuserreport->sortitemid)) {
+            if (isset($SESSION->gradeuserreport->sortitemid) && in_array($SESSION->gradeuserreport->sortitemid, $namefields)) {
                 $this->sortitemid = $SESSION->gradeuserreport->sortitemid;
             } else {
-                $this->sortitemid = 'lastname';
+                $this->sortitemid = end($namefields);
             }
 
             if (isset($SESSION->gradeuserreport->sort)) {
diff --git a/grade/report/lib.php b/grade/report/lib.php
index a49effe5746dd..99e805d7ab184 100644
--- a/grade/report/lib.php
+++ b/grade/report/lib.php
@@ -466,13 +466,14 @@ public function setup_users() {
         $filtersurnamekey = "filtersurname-{$this->context->id}";
 
         $this->userwheresql = "";
+        $usernamefields = core_user::get_user_full_name_fields();
         $this->userwheresql_params = array();
         if (!empty($SESSION->gradereport[$filterfirstnamekey])) {
-            $this->userwheresql .= ' AND '.$DB->sql_like('u.firstname', ':firstname', false, false);
+            $this->userwheresql .= ' AND '.$DB->sql_like('u.' . reset($usernamefields), ':firstname', false, false);
             $this->userwheresql_params['firstname'] = $SESSION->gradereport[$filterfirstnamekey] . '%';
         }
         if (!empty($SESSION->gradereport[$filtersurnamekey])) {
-            $this->userwheresql .= ' AND '.$DB->sql_like('u.lastname', ':lastname', false, false);
+            $this->userwheresql .= ' AND '.$DB->sql_like('u.' . end($usernamefields), ':lastname', false, false);
             $this->userwheresql_params['lastname'] = $SESSION->gradereport[$filtersurnamekey] . '%';
         }
 
diff --git a/lib/classes/user.php b/lib/classes/user.php
index 06fa5f4c15819..0521694c3148e 100644
--- a/lib/classes/user.php
+++ b/lib/classes/user.php
@@ -1716,6 +1716,42 @@ public static function get_name_placeholders(stdClass $user): array {
         }
         return $namefields;
     }
+
+    /**
+     * Retrieves the fields used for displaying a user's full name in the system.
+     *
+     * This function extracts the placeholder fields from the configured full name display format and
+     * returns them as an array.
+     *
+     * @param array $options optional array for override.
+     * @return array List of field names used in the full name display format.
+     */
+    public static function get_user_full_name_fields(array $options = []): array {
+        global $CFG;
+        $override = $options["override"] ?? false;
+        // Get all of the name fields.
+        $template = null;
+        // If the fullnamedisplay setting is available, set the template to that.
+        if (isset($CFG->fullnamedisplay)) {
+            $template = $CFG->fullnamedisplay;
+        }
+        // If the template is empty, or set to language, return the language string.
+        if ((empty($template) || $template == 'language') && !$override) {
+            $fullnamedisplay = get_string('fullnamedisplay');
+        }
+        // Check to see if we are displaying according to the alternative full name format.
+        if ($override) {
+            if (empty($CFG->alternativefullnameformat) || $CFG->alternativefullnameformat == 'language') {
+                // Default to show just the user names according to the fullnamedisplay string.
+                $fullnamedisplay = get_string('fullnamedisplay');
+            } else {
+                // If the override is true, then change the template to use the complete name.
+                $fullnamedisplay = $CFG->alternativefullnameformat;
+            }
+        }
+        preg_match_all('/{\$a->(.*?)}/', $fullnamedisplay, $matches);
+        return $matches[1];
+    }
 }
 
 // Alias this class to the old name.
diff --git a/lib/table/classes/flexible_table.php b/lib/table/classes/flexible_table.php
index 9d52cad337374..71725cdf95ea4 100644
--- a/lib/table/classes/flexible_table.php
+++ b/lib/table/classes/flexible_table.php
@@ -20,6 +20,7 @@
 use core_table\local\filter\filterset;
 use core\exception\coding_exception;
 use core\output\renderable;
+use core_user;
 use html_writer;
 use moodle_url;
 use paging_bar;
@@ -688,12 +689,13 @@ public function get_sql_where() {
             static $i = 0;
             $i++;
 
+            $usernamefields = core_user::get_user_full_name_fields();
             if (!empty($this->prefs['i_first'])) {
-                $conditions[] = $DB->sql_like('firstname', ':ifirstc' . $i, false, false);
+                $conditions[] = $DB->sql_like(reset($usernamefields), ':ifirstc'.$i, false, false);
                 $params['ifirstc' . $i] = $this->prefs['i_first'] . '%';
             }
             if (!empty($this->prefs['i_last'])) {
-                $conditions[] = $DB->sql_like('lastname', ':ilastc' . $i, false, false);
+                $conditions[] = $DB->sql_like(end($usernamefields), ':ilastc'.$i, false, false);
                 $params['ilastc' . $i] = $this->prefs['i_last'] . '%';
             }
         }