The Comprehensive School Mathematics Program (CSMP) is a program of CEMREL, Inc., one of the national educational laboratories, and was funded by the National Institute of Education (NIE). Its major purpose is the development of curriculum materials for grades kindergarten through 6. At the end of the 1978-1979 school year, a series of tests was administered to fourth-grade CSMP classes and comparable non-CSMP classes. Two-thirds of those CSMP classes which had been using the program as their regular curriculum since at least the second grade were included. Among the results, non-CSMP classes did better, at the .05 level of significance, on the Stanford Achievement Test, while CSMP pupils did significantly better on the other computation scales, as well as on measures of mental arithmetic and fractions. Analysis indicates results consistent with those from other grade levels, and appears to indicate that CSMP promotes improvement in several mathematical thinking processes viewed as important, with minimal loss in the usual areas of study. (MP)