The purpose of the research is to find out the influence of training method and group cohesiveness to the effectiveness of decision making. Learning strategy training and group cohesiveness serve as independent variable while decision-making effectiveness variable is the dependent variable. The sample of the research is ninety teachers chosen randomly from cluster sampling of 120 teachers from 18 private accredited A senior high schools in Bekasi city. Hypothesis testing was conducted on the level of significance 0.05. The research method used is an experiment and the technical analysis used is a two-way ANOVA. The study concludes that there is an influence between learning strategy training process of problem-based learning and expository learning into the effectiveness of decision making. There is also an impact on group cohesiveness and the efficiency of decision making, and there is influence on mutual interaction between learning strategy training method, expository learning, and group cohesiveness into the effectiveness of decision making.