Many studies have been conducted to assess the effects of the ISCS program on student performance. On the basis of the conflicting findings, the task of arriving at a general conclusion about the effects of ISCS has been difficult indeed. This study was designed to integrate quantitatively the collective research dealing with the effects of ISCS on student performance and attitude. The weighted mean effect size was found to be 0.09, indicating that the performance of the ISCS students was 0.09 standard deviations above the performance of students in traditional science courses. The design of the study accounted for a significant proportion of variation in the effect size, whereas the type of instrumentation and reliability of the instrument did not.