It is a violation of the B visitor status to enroll in a course of study while in that status. If you enter the United States on a visitor’s visa or change status to B and wish to attend school, you must file for a change to student status and wait for that status to be approved before beginning school. Or, you may leave the U.S., apply for an appropriate student visa abroad, and return in proper student status.
From time to time, people whose primary plan was to attend school, have used the visitor visa to enter the U.S. by “pretending” that they were coming only to visit. They believed that it was easier to get the visitor visa or feared that the student visa might be denied. So, in a word, they lied about their plans to the consular officer and to the officer at the port of entry. This has made it impossible or highly unlikely that a change of status would be approved, and they have ended up having to return home in order to obtain the student visa and return for a later term.
If you are really coming to look at schools or to make decisions about which school to attend, you must be honest and say so at the port of entry. The USCBP officer will make a notation in the immigration records that you have entered as a “prospective student.” That notation will permit an officer at a USCIS service center to approve a change of your status from visitor to student. Without that notation, the USCIS officer will not be permitted to change your status and you will have to leave the U.S. and get a student visa. Do keep in mind that the change of status must be approved before you can begin your studies and that the process may take several months.