protected function set_columns() {

		$cols = array(
			'id'         => array(
				'exportable' => true,
				'title'      => __( 'ID', 'lifterlms' ),
				'sortable'   => true,
			),
			'quiz'       => array(
				'exportable' => true,
				'title'      => __( 'Quiz', 'lifterlms' ),
				'sortable'   => false,
			),
			'course'     => array(
				'exportable' => true,
				'title'      => __( 'Course', 'lifterlms' ),
				'sortable'   => false,
			),
			'lesson'     => array(
				'exportable' => true,
				'title'      => __( 'Lesson', 'lifterlms' ),
				'sortable'   => false,
			),
			'attempt'    => array(
				'exportable' => true,
				'title'      => __( 'Attempt #', 'lifterlms' ),
				'sortable'   => true,
			),
			'grade'      => array(
				'filterable' => llms_get_quiz_attempt_statuses(),
				'exportable' => true,
				'title'      => __( 'Grade', 'lifterlms' ),
				'sortable'   => true,
			),
			'start_date' => array(
				'exportable' => true,
				'title'      => __( 'Start Date', 'lifterlms' ),
				'sortable'   => true,
			),
			'end_date'   => array(
				'exportable' => true,
				'title'      => __( 'End Date', 'lifterlms' ),
				'sortable'   => true,
			),
		);

		return $cols;
	}