The Incredible Years Teacher Classroom Management (IY-TCM) program is an evidence-based intervention intended to promote the social and emotional skills of children and to reduce the frequency of inappropriate types of behavior. This paper reports on its initial implementation in Portugal. The primary aim of this study is to establish preliminary evidence on the social skills of Portuguese children and behavioral difficulties at school and on teacher practices concerning the IY-TCM as a universal stand-alone intervention. Additional aims are to determine whether is effective in a subsample of children at risk of developing behavioral disorders and to assess its acceptance by Portuguese preschool teachers. Eight pre-school teachers who received IY-TCM training were compared to eight corresponding teachers who did not. A total of 296 children, aged 3-6 years old, took part in the experiment. Overall, the results from this study suggest that the IY-TCM program had resulted in changes in the expected direction at child level (including children with early signs of disruptive behavior) and at teacher level, with medium and high effects sizes. Teacher satisfaction with numerous aspects of the IY-TCM program was high.