While research efforts have determined that decision making is of major importance in lesson planning, there has been little work that systematically explores the effect of training in decision making on lesson planning, particularly in terms of preservice teachers. This study used four computer simulations designed to teach decision making skills in an effort to determine whether students' lesson planning ability would be affected after working through the simulations. Eighty-two students were divided into two groups: those just beginning their teacher education, who had no experience in lesson planning, and those in their senior year of study, who had some experience in lesson planning. Each student was required to write two lesson plans. Half of each group worked through the computer simulations after they wrote the first lesson plan and before they wrote the second. The two lesson plans were then compared for differences. There were nonsignificant differences in the number of characteristics found in the lesson plans of those students who used the computer simulations and those who did not. There were more characteristics in the second lesson plans of the senior students than in those of the novices. Also, those who had successfully followed the decision paths in the computer simulations had more complete lesson plans than those who were unsuccessful. These results suggest that decision making training is best utilized with advanced students. Statistical tables are included. (JB)