SETting values to TABLE field at TRIGGER runtime

[Ferindo Middleton Jr]

Is it possible to SET values on fields that involve the TABLE that 
invoked the TRIGGER with SET actions.
I have the following lines in my trigger:

delimiter //
CREATE TRIGGER trigger_registration_and_attendance_before_insert
BEFORE INSERT
ON registration_and_attendance
FOR EACH ROW
BEGIN
    DECLARE schedule_class_id INT;
    DECLARE schedule_class_id_cursor CURSOR FOR SELECT class_id FROM 
schedules WHERE schedules.id =                                         
new.schedule_id;
    FETCH schedule_class_id_cursor INTO schedule_class_id;
    SET new.class_id = schedule_class_id;
END;

The server accepts this but "new.class_id" doesn't get a value when I do 
an INSERT. Why won't this work?

Ferindo