This study was primarily concerned with whether Cooperative Integrated Reading and Composition (CIRC), which uses cooperative learning with an integrated language arts program, had a greater impact on student achievement than an integrated language arts program which uses non-cooperative learning procedures. Of further interest was the effect on student achievement of teachers' fidelity of implementation of CIRC and their concerns while implementing this new methodology. This quasi-experimental study involved 310 students of 24 teachers at grade three and 320 students of 18 teachers at grade five.