Can an employer require you to work outside of normal hours and not pay the staff?

This depends on your job duties.  If your main role is teaching preschool, you may be exempt from the minimum wage and overtime laws as a “professional.”  If you are an aide or other type of administrative assistant, you may be entitled to overtime.  Further, if you are not exempt and are paid by the hour, as a matter of contract, the employer typically has to pay you for all hours worked, including the graduation, if the company requires you to be there.