The purpose of this study is to investigate the effects of case teaching on how students learn about genetic engineering, in terms of meaningful learning and retention of learning. The study was designed as quasi-experimental research including 63 8th graders (28 boys and 35 girls). To collect data, genetic engineering achievement tests were developed by the researchers and concept maps (CMs) were used. In the study, the experimental group (n = 31) experienced case teaching, while the comparison group (n = 32) experienced ordinary teaching. To analyse the data from achievement test scores, the Wilcoxon signed-rank test and the Mann-Whitney U test were used. In analysis of the CMs, the number of concepts, number of connecting phrases, number of examples used in the maps and shape of the maps were determined. The analyses showed that the mean achievement scores of the groups significantly differed in favour of the experimental group. Also, retention of the learning in the experimental group was observed. The number of concepts used in CMs did not significantly differ, while the number of connecting phrases in both groups differed significantly in favour of the experimental group. In addition, the students in the experimental group changed their initial hierarchical maps into branched maps, indicating more connection to other concepts.