Economic Knowledge is an important factor which can solve the economic problems in our lives. However, it is not easy for students to learn the economic knowledge in class and to put the knowledge to practical use in solving the economic problems. Especially, learning the economic knowledge that they have not experienced in their daily lives, they feel all the more difficult. The purpose of this study is to design classroom experiment model as the teaching-learning method to fully understand the hard experienced economic knowledge and to test its effect through the experiment. The use of economic experiments in the classroom enables students to experience the functioning of markets and to discover principles of economics in a laboratory setting. Therefore, the economic knowledge is fully understood in classroom experiments model, not simply memorized as an ambiguous idea. Based on this theoretical foundation, the hypothesis of this study is as follows: The understanding score of the subjects with classroom experiment on the effects of sales taxes will be higher than that of the subjects without it. For the test of this hypothesis, the subjects consisted of 205 middle school students. The results of data have been analyzed by multiple regression. The test result was that it is effective to use the classroom experiment as model of economics lesson in middle school. Classroom experiment helped students to fully understand the hard experienced economic knowledge, the effects of sales taxes, and to use the knowledge in other situations. The result suggests that it is necessary to develop other appropriate calssroom experiment models for economics lesson. It is certain that these studies can be helpful for the improvement for the economic education.