DS 2019 form
DS-2019 is a document on the basis of which one applies for the visa. Each student registered for the program, when entering the Embassy, has to have this form. It has to be signed and be kept during the travel and stay in the USA, the same as with visa. Your visa is not valid without this form. DS-2019 has to be carried with the passport all the time during the program duration.
If there is a difference between the date when the visa started to be valid and the date when the program starts on the DS-2019 form, (even though these dates match in the most cases) candidate is obliged to stay in the USA until the date, which is given in the form I-94 which one gets when they enter America. If the candidate loses DS-2019, they are obliged to inform the agency representative or the company itself which is the program organizer in America.