I arrived in the United States four months ago as a tourist on a B-2 visa, which has "prospective student" in the annotation at the bottom. The officer at the airport gave me a six-month period of stay. While here, I visited a few universities and decided to pursue a master's degree. The university that I hope to attend helped me apply for a change of status from B-2 to F-1 status. My six-month stay expired a week ago, however, and I still don't have the F-1 approval yet. My classes are set to start in a month. It seems like I'm out of status. Now what?
As you're likely aware from talking with your university's international student office, you first need to be approved for F-1 status before starting your studies. One of the basic requirements to change immigration status, such as from B-2 tourist to F-1 student, is that you maintained the last status you had. In your case, as long as you have been doing solely tourism- or visitor-related activities, you meet this requirement.
Another key requirement to changing status is that you must submit the application (on Form I-539) before your current status expires. In your case, you appear to have complied with this, since you state that you submitted your F-1 change of status application during your six-month B-2 visitor period. The pending application allows you to remain in the United States while awaiting the approval.
You technically do not have any lawful status now, but you are authorized to be here. It's somewhat of a middle ground between maintaining status and not maintaining status. If U.S. Citizenship and Immigration Services (USCIS) were to deny the F-1 change of status application, you might need to leave the country. On the other hand, upon approval of the application, your status simply will change from B-2 visitor to F-1 student.
To ensure that your eligibility for a change of status will not be questioned, it's important that you not enroll in classes or work without authorization. Either of these will make you ineligible to change status and could lead to a denial of the application.
Finally, keep in mind that the next time you travel outside the U.S. after you have your F-1 change of status approved, you will need to obtain an F-1 visa from the U.S. consulate before returning. (USCIS has no power to give you the actual F-1 visa that’s required for U.S. entry.)
Also, if your F-1 change of status application is denied, you still may have the option of obtaining the F-1 visa abroad and then returning to start your studies.