public function on_gradebook_end() {

        $this->open_xml_writer('gradebook.xml');
        $this->xmlwriter->begin_tag('gradebook');
        $this->write_grade_categories();
        $this->write_grade_items();
        $this->write_grade_letters();
        $this->xmlwriter->end_tag('gradebook');
        $this->close_xml_writer();
    }