This study examined the effect of classroom climate on the mathematics achievement of fourth-grade students in Tennessee public schools. The investigation used data obtained from 875 fourth-grade students enrolled in 42 classes in 13 public schools. In the first phase of the inquiry, four class-climate factors were identified by exploratory factor analyses of 44 items comprising a classroom climate inventory. The four factors were labeled as academic orientation, satisfaction, class tension, and cohesiveness. Subsequent reliability analyses established both student and class level reliability estimates of the climate measures. In the second phase, effects of climate factors on class mean achievement and on relationships between achievement and student variables were assessed with a two-level hierarchical, linear model. Results indicated that: (1) class-climate factors affect mathematics achievement differently depending on student characteristics; (2) distribution of achievement varies as a function of class climate; (3) climate factors mediate associations between student characteristics and mathematics achievement; and (4) higher and more equitable distributions of achievement exist in classes with higher levels of academic emphases and student satisfaction, as well as in classes with low levels of tension. (72 References) (Author)