The Customs and Border Protection (CBP) officers make the final determination to allow you entry to the U.S. If you or your dependent(s) arrive at a border in good faith but without a proper I-20 or DS-2019, or without a valid travel signature, the officer may grant you temporary entry for 30 days and issue you a form I-515A.
If you receive this form you must make an appointment with your adviser in the Office of Global Initiatives (OGI) right away. You have 30 days to send the required documentation to SEVP or your SEVIS record will be terminated.
Study in the States provides more information on the Form I-515A.