Two studies evaluated a comprehensive cooperative learning approach to elementary reading and writing instruction, called Cooperative Integrated Reading and Composition (CIRC). The subjects in the first study, 461 third- and fourth-grade students in a suburban Maryland school district, were divided into experimental and control groups, with the experimental CIRC groups working in heterogeneous learning teams for all reading, language arts and writing activities. In reading, CIRC students worked with partners during follow-up times on partner reading, decoding, story structure, prediction, and story summary activities related to the basal stories. In writing and language arts, CIRC students used a process approach to writing and peer conferences during planning, revising and editing stages of the process. Subjects in the second study, 450 third- and fourth-grade students were chosen from a wider range of ethnic and socio-economic backgrounds than those in the first, although the second study was an extension and replication of the first. The results of both studies show significant effects in favor of the CIRC students on standardized test measures of reading comprehension, reading vocabulary, language mechanics, language expression and spelling. Also noted were effects favoring CIRC students on writing sample and oral reading measures. (Six tables of data are included, and 51 references are attached.) (NH)