The purpose of this research was to conduct a preliminary analysis of a new instrument, the Classroom Environment Index (CEI), designed to measure the psychological environment (press) of the classroom. The structure was essentially the same as other Syracuse indexes, containing 30 scales of 10 items each. Three forms of the instrument were developed. The third revision exhibited adequate reliability and homogeneity, and differentiated between classrooms, subjects, grades, and educational levels. Six first-order and two second-order factors were extracted. Eventually, the CEI will be used to examine relationships between classroom press and student achievement. (Author)