The purpose of this study was to examine the effects of heterogeneous groups for cooperative learning on students' cognitive and affective performance in anchored instruction. Forty-two fifth graders participated in this study. They were divided into gender-heterogeneous combinations: two boys plus one girl vs. two girls and one boy. Four dependent variables were measured, including problem- solving strategies, learning transfer, attitudes toward mathernatics and attitudes toward cooperative learning. Results from t-tests indicated there were no significant difference between two heterogeneous groups. This study was funded under the support of National Science Council (grant number NSC86-2511-S-032-003).