The present study is the result of implementing an antisocial behavior prevention program in preschool education. The intervention goal was to prevent the emergence of antisocial behaviors through developing social competence in the participants. The program, called Aprender a Convivir, is divided into four modules by topic: rules and rule-following, emotions and feelings, communication skills, and helping and cooperation skills. The intervention was carried out during the academic year 2007-2008. The sample was composed of four-year-old pupils (n=147) divided between a control group (n=69) and an experimental group (n=78). Results were obtained by administering the Child Behavior Checklist-Teacher Report Form (CBCL-TRF) and the Preschool and Kindergarten Behavior Scales (PKBS) for teachers and parents. Results show a noteworthy reduction in antisocial behaviors and a substantial improvement in social competence among experimental group members. (author abstract)