*/
	protected function set_columns() {
		return array(
			'id'       => array(
				'exportable' => true,
				'title'      => __( 'ID', 'lifterlms' ),
				'sortable'   => true,
			),
			'title'    => array(
				'exportable' => true,
				'title'      => __( 'Title', 'lifterlms' ),
				'sortable'   => true,
			),
			'course'   => array(
				'exportable' => true,
				'title'      => __( 'Course', 'lifterlms' ),
				'sortable'   => false,
			),
			'lesson'   => array(
				'exportable' => true,
				'title'      => __( 'Lesson', 'lifterlms' ),
				'sortable'   => false,
			),
			'attempts' => array(
				'exportable' => true,
				'title'      => __( 'Total Attempts', 'lifterlms' ),
				'sortable'   => false,
			),
			'average'  => array(
				'exportable' => true,
				'title'      => __( 'Average Grade', 'lifterlms' ),
				'sortable'   => false,
			),
			'actions'  => array(
				'exportable' => false,
				'title'      => __( 'Actions', 'lifterlms' ),
				'sortable'   => false,
			),
		);