Full time student can refer to either high school or college. Full time student for the purpose of taxes means that the student was enrolled in a school for at least one day of at least five months of the year. It is not based on the course load of the school.
The Form 1098-T is issued by educational institutions showing the amount of tuition that was paid during the year, as well as other information about the student's enrollment in the school. It is typically issued by colleges, not high schools.
@sonorat123