The Stop & Think Social Skills Program was implemented as a stand-alone primary prevention program using a sequential cohort design with two cohorts of kindergarten students. Cohorts were assessed at pretest and posttest using the Social Skills Rating System Teacher Questionnaire. Students in Cohort 1 showed improvement in Social Skills, Academic Competence, and Problem Behaviors. Comparison of posttest scores in this cohort with pretest scores collected at the same time for Cohort 2 indicated that these changes were unlikely to be caused by maturation. Cohort 2 also showed improvement in Social Skills and Problem Behaviors following implementation of the program but did not show a statistically significant change in Academic Competence. In addition, changes in specific academic skills were not consistent across cohorts. Measures of treatment integrity indicated the program was implemented as designed. Social validity ratings by teachers revealed that they believed the intervention enhanced students' social skills, but teachers were concerned about the length of the program and students' understanding of program content. Limitations of the study and the implications of these findings for school psychology are discussed. (Contains 2 tables.)