Escaped variable in the sql query

~dev_rating/application/classes/Model/Teachers.php

@@ -55,8 +55,9 @@ class Model_Teachers extends Model
      * @return Database_Result select from <tt>view_disciplines_teachers</tt> table
      */
     public static function ofDiscipline($id) {
-        $sql = "CALL `GetTeachersForDiscipline`('$id'); ";
-        return DB::query(Database::SELECT, $sql)->execute();
+        $sql = "CALL `GetTeachersForDiscipline`(:id)";
+        return DB::query(Database::SELECT, $sql)
+            ->param(':id', $id)->execute();
     }
 
     public static function getNamesForDiscipline($disciplineID, $asConcat = false, $asAbbreviation = false) {