ON DELETE CASCADE

[Anette B]

Hi,
I have added my first two MySQL tables:
CREATE TABLE a (
id int NOT NULL AUTO_INCREMENT, PRIMARY KEY(id),
content varchar(20) NOT NULL,
done date NOT NULL
)
CREATE TABLE w (
id int NOT NULL AUTO_INCREMENT,
PRIMARY KEY(id),
swedish varchar(20) NOT NULL,
english varchar(20) NOT NULL,
assignment_id int NOT NULL,
INDEX fk_assignmentid (assignment_id),
FOREIGN KEY (assignment_id) REFERENCES assignment(id) ON DELETE CASCADE
)

I have added data to both tables, so that the value in column assignment_id in table w corresponds to the value in column id in table a.
When I delete the record in table a, shouldn't the records in table w that has correspondning values also be deleted automatically?
That doesn't happen...