The main purposes of this experimental study were threefold, firstly,to find an appropriate training method for increasing the belief in internal locus of control in perteen children. Secondly, to indicate the amount of time for effective training, and finally, to identify the type of trainees who were suitable for the training. Thus, there were three research objectives of this study,  firstly, to examine the consequences of employing token economy technique for the development of belief in internal locus of control of reinforcement and mental health of children. Secondly, to compare the belief in internal locus of control and mental health of the children with different amount of achievement motivation who were in the token economy or the non-token economy coditions. Finally, to compare the belief in internal locus of control and mental health of the children who reported receiving different amount of resoning oriented child-rearing practices who were in the experimental or the control conditions mentioned above. 
                The sample in the study consisted of 154 boys and girls, whose age ranged from 10 to 13 years, from two elementary schools in Nakhonrachasrima Province. the pupils in each school were  randomly assigned to one of the four conditions, which were the four combinations of contracting technique  and systematic rewarding techinque. In the other words, the token economy condition consisted of both contracting and systematic rewarding techniques, contracting condition consisted of contracting and non-systematic rewarding techniques, systematic rewarding condition consisted of non-contracting and systematic rewarding conditions, and control group consisted of no-contracting and non-systematic rewarding conditions. Each pupil participated in the 3 sets of game, wich required effort, and the players were rewarded according to the condition he or she was randomly assigned to. The pupils in each condition were trained for fifteen periods, each of which took 30-60 minutes on each consecutive day. The assessments of the belief in the locus of control and mental health were carried out 3 times after one-thirds, two-thirds and all of the games were played. 
                    Seven different sets of questionnaires were designed to assess the fallowings : resoning - oriented practices, achivement motivation, background characteristics, belief in internal locus of control (trait and state), mental health and the manipulation check. The first three sets of questionnaires were used to assess the 3 independent variables and the others were used to assess the dependent variables. 
                     Six hypotheses were tested using the Analysis of  Variance with 3-way factorial designs and 3-way with one repeated measure design, the Stepwised Multiple Regression Analysis and intercorrelation matrices on the data of the total sample as well as on the data of different subgroups of respondents, classified by the bio-social and background variables. 
                   There were two major groups of findings in this experimental study. First it was found that with increasing periods of training the pupils in the token economy condition showed increasing amount of the trait of  belife in internal locus of control while the state characteristic remained constant constant but the anxiety level and aggression scores were lower. In the contracting condition, however, the state specific type of internal control was reduced and at the same time the total mental ill-health and aggression were heightened with increasing time of training. In the other two conditions, namely, the systematic  rewarding and the control conditions, the results were inconsistent. Therefore, this part of the data showed that the token economy condition was the most effective in inducing belief in internal locus of control and in promoting mental health of the pupils. 
                   Another section of the data showed that the pupils who were assigned to the token econony condition (in comparison with the control group) and the pupils who were given systematic rewards (in comparison with the ones who were given unsystematic rewards) when measured the first time (after playing the games for 5 out of 15 periods), the pupils in these two conditions scored higher on the internal locus of control (state) measure than their control peers, but these same groups of pupils showed greater mental ill-health than their control peers. These findings were pervalent among the pupils with high academic achievement high need for achievement and among those who reported receiving high reasoning oriented child-rearing practices. However, two weeks after the training period was over, when the psychological measurements were repeated for the third time, it was found that the various aspects of mental ill-health were not significantly different among the pupils in the four experimental conditions.  Nevertheless, the trait of internal control of the pupils in the token economy condition and the systematic rewarding conditions were higher than the comparing conditions mentioned above, especially among the female subsample. In addtion, it was found that the variable of contracting was one of the 3 most predictive factors of the general trait of belief in internal locus to control. Unexpectedly, it was found that pupils who received the contract scored lower in the general trait of internal control, at the end of the experiment. On the other hand, the systematic rewarding variable was the best predictor of the belief in internal locus of control (state specific) such that the puils in the systematic 
rewarding condition were higher scoreres on the test of belief in internal locus of control than the pupils in the non-systematic rewarding conditions. 
               According to the results in this experiment it could be suggested that the technique of token econany can be used to heighten the belief in internal locus of control of reinforcement as well as the behaviors of thai pupils, especially the female pupils. In addition, for the rural elementary school pupils the technique of token economy should be applied for at least 15  conseccutive periods. This technique will be highly beneficial for use in elementary school for hunan resource development in Thailand.