Classroom experiments can play a significant role as a useful and innovative teaching tool in economic education as well as in the natural sciences. Evidence indicates that experiments supplement and reinforce materials presented in a traditional lecture format, and that the use of economic experiments in instruction has a positive impact on students\' learning of economics. On the other hand, the opportunity cost of using the experiments is also substantial. Consequently, the cost-benefit considerations lead to the conclusion that instructors must be selective when choosing topics to teach. Although one of the main aims to teach economics is to enable students to behave rationally, irrational economic behaviors in terms of sunk cost are easily found. Sunk cost is an expenditure that has already been made that cannot be recovered. Therefore, sunk cost in terms of money, effort, or time, should not influence the present decision. However, there is a great tendency for a prior expenditure to continuously influence the present decision. A total of 199 students participated in the experiment, and a maximum of 5 points were given to them as an incentive. The results show that only 50.3% made a rational decision. The remaining 99 subjects, 49.7% took sunk cost into consideration of present decision. Given the single and well defined experimental scenario, the sunk cost effect is accepted. But male-female differences in the sunk cost effect were not found in the results. Finally, the sunk cost effect was significantly lessened by having taken a prior lecture on the concept of sunk cost.