Pre-existing misconceptions are serious impediments to learning in mathematics. Means for detecting and correcting them have received much attention in the literature of educational research. Dynamic geometry software has been tried at different grade levels. This quasi-experimental study investigates the effect of Cabri-assisted instruction on tenth graders' misconceptions about graphs of quadratic functions. The results indicate that Cabri-assisted instruction did not have a statistically significant effect on their misconceptions, but the misconception scores of the experimental group were better than those of the control group. Also, there was a significant difference between the achievement scores of the two groups. Scores of the experimental group on a quadratic functions test were significantly higher than those of the control group. In conclusion, some implications and limitations of the study are discussed. (Contains 4 tables and 3 figures.)