There are two procedures on the System homepage which create new households for students after they leave your school: Create Alumni Households and Create Former Student Households.
These procedures are typically run during the summer months between school years but — for some reason or another — it sometimes isn't run until after the summer months end. You may wonder about data integrity and be concerned that it is a problem to run these procedures if the new school year has already started.
You do not need to worry. These procedures look for Alumni or Former Students who are not in their own households and creates new households for them. Neither of these procedures affect students and, therefore, can be run at any time.