Even though the International Olympiad in Informatics directly involves a restricted number of pupils from each country, one of its primary goals is stimulating interest in computer science and information technology over the whole younger segment of the world' s population. In several countries, this aim has to be accomplished without an active intervention of the Ministry of Education on school programs, relying on the efforts of small devoted organizations. In this context, promoting the involvement of a large number of school teachers may be as crucial as difficult to achieve. Following a 9-year experience of teams competitions in Italy, recently shared with other European countries, we argue that teams Olympiad may be an effective tool for widening the participation of high-school students and teachers, synergistically cooperating with existing individual competitions. On the one hand, teams contests foster peer education, encouraging talented students to help training fellows. On the other hand, these competitions can be more appealing both for average students, valuing group membership more than personal accomplishments, and most importantly, teachers: team achievements are more recognizably linked with the overall school or teacher performance than solitary excellences, resulting in increased returns rewarding the involved subjects.