Full-time status is determined by the school. You are full-time if they consider you full-time, so you have to ask the school. You have to have been full-time for some part of each of 5 calendar months during the year. The 5 months do not have to be consecutive.
Note that, for the child and dependent care credit, your full-time student status doesn't count unless your spouse was working during the same month that you were a full-time student.
