When a foreign national is applying to school in the United States he or she must obtain an I-20 form from the college in addition to acceptance by the school. That form is taken to a US consulate (along with evidence of ability to support yourself while in school and pay for tuition and evidence of ties to your home country) to obtain a student (F-1) visa which will be issued for the duration of student status (D/S). If you decide to visit schools in the US in Visitor (B-1/2 status) make sure that is annotated on your I-94 (Arrival/Departure document) in case you wish to change status to F-1 while in the United States. Since September 11, 2001, USCIS has been reluctant to allow foreign nationals to change to student status in the U.S.