The main purpose of this study was to investigate the effects of a case study approach on students' achievement and attitudes towards viruses, bacteria, fungi, and protista. Fifth-grade students (N = 88) from two different classes were involved in the study. One intact class was assigned as the experimental group, whereas the other intact class was assigned as the comparison group. The comparison group students received their instruction by traditional teaching, whereas the experimental group students were instructed with a case study approach. Achievement and attitudes were measured before and after instruction. Results revealed that there were significant differences favoring the case study approach on students' achievement and attitudes towards science. (Contains 3 figures and 2 tables.)