A student-teacher ratio expresses the relationship between the number of students in a given classroom to the number of full-time teachers. In blended and personalized environments, a “classroom” size can vary significantly. For example, in some cases, a class might be traditionally sized, with one teacher working with a group of 25-30 students. In other cases, a group of teachers might be working in a more open classroom with a whole grade of 80 students.