To delete your sim's homework, bring up the cheat menu ( ctrl+shift+c ) and type in 'moveobjects on'. Then when your sim comes from school and puts his of her homework on the ground, go to buy mode and pick up the homework book. Although you wouldn't be able to delete it directly, you could put it on a desk or a table, etc. then delete the desk or the table. Todah! Homework's gone! And your sim wouldn't lose a grade or get into trouble.