You shouldn't procrastinate at school.
Sandra has been given an assignment to do in class which she is supposed to hand in at the end of he period.
Sandra wants to start her assignment.
Sandra starts the assignment immediately and has ample time to finish it before class ends.
Sandra doesn't feel like doing the assignment and doesn't start it until half way through the period.
Sandra does well on the assignment and gets a good grade on it.
Sandra doesn't manage to finish the assignment by the end of the period and gets a low grade for the work.