This shows the number of students per full-time teacher. A low student-teacher ratio is not the same as a small class size. Some schools have teachers who teach specialized subjects with smaller classes. Other schools hire extra teachers to free up class preparation time for their core teaching staff. Both of these possibilities lower the overall student-teacher ratio but not the average class size.
Source: GreatSchools calculated this ratio by dividing the number of students enrolled by the number of full-time teachers. Student enrollment and full-time teacher count were provided by the Ohio Department of Education and are from 2007-2008.