The first seven days of a semester (or the first three days of the summer session) is the add/drop period, in which you can adjust your courses to best fit your interests and academic goals. During open registration for the subsequent semester and during the open reregistration period immediately prior to the semester's beginning, you may add and drop classes in APR2. After this, you must use an add/drop form, which requires the signatures of your academic advisor and all instructors whose classes you wish to add or drop. The add/drop form must be submitted to the registrar's office (Vilas 117) by the deadline.
If you fail to submit the add/drop form on time, you may petition after the deadline to add/drop a course that you have/have not been attending, so that your enrollment status properly reflects the reality of the courses you are in fact taking. If your petition is approved, you will be assessed a late schedule change fee.
Once the add/drop period has ended, you are expected to stay in the courses for which you have enrolled for the entire semester. However, if you find yourself in serious academic distress in a course after this deadline, you may withdraw from a course. Unlike in the case of add/drop, a course you have withdrawn from remains listed on your transcript, but with the notation "W" denoting the withdrawal. It does not contribute to your GPA, nor does it contribute credit toward graduation. You may withdraw from a maximum of two courses during your time at St. Lawrence.
Note that you may not drop a course you have been attending after the add/drop period is over. You are enrolled in the course at that point, so you must withdraw if you wish to get out of the course.