An early complication in measuring the efficacy of class size reduction was the tendency for different ideological camps to use different definitions of class size in the literature. As a direct measure of the number of students in each class, group size is currently understood by the educational community to be the best measure of a teacher's "true opportunity to build direct relationships with each student." A more malleable definition and one now held in dubious regard,[4] pupil to teacher ratio, would declare a situation in which one teacher leads a class while another does paperwork in the back but does not interact with students as being half as large as its group size.[14]
In the past, depending on which measure was used, researchers tended toward far different interpretations of the benefits of class size reduction leading to far different recommendations for implementation. In 2002, Margaret Spellings, secretary of education under President George W. Bush, pointed out the need for a standardized definition of what is meant by class size.
To differentiate student-teacher ratio and class size, it is important to know several key distinctions. Class size, generally speaking, refers to the average class size in a given grade level of a given school. Student-teacher ratios, normally, are calculated by taking the total number of teachers at a given school divided by the complete enrollment of that school. This distinction is significant, because the ratio will not always match up with the class size figure (or vice versa). For example, a student-teacher ratio may be small but a class size may be larger than what the student-teacher ratio leads one to believe.[15]