This study aimed to find out the effectiveness of constructivism-based
CIRC of cooperative learning on students' mathematical communication skills and
self-efficacy. This research is an experimental study with a posttest-only control
design research design. The population in this study were all grade VII students of
SMP Negeri 1 Sumbang. Sampling was determined using cluster random
sampling techniques and it obtained class VII G as an experimental class using
cooperative learning type CIRC based on constructivism and class VII F as a
control class using conventional learning. Data analysis on hypothesis testing
used the Independent Sample T-Test with the right side of the test on the post test
and questionnaire with α = 0.05. The Sig. of the post test was 0,000 and Sig. in a
questionnaire was 0.015. Therefore, it can be concluded that the CIRC type of
constructivism-based cooperative learning affected the mathematical
communication skills and self-efficacy of students of SMP Negeri 1 Sumbang.