The aim of the present article was to investigate the outcomes of the universal social competence promotion program Second Step in a typical `real world' implementation in Norway. We addressed the effects of the program on social competence and externalizing and internalizing problem behaviour among 1,153 fifth and sixth grade students (11 schools, 55 classrooms) after one year of intervention. Although the program is originally American, Second Step has been translated and adapted for the Norwegian setting and renamed Steg for Steg. Applying Linear Mixed Modelling, the results from the age cohort design with comparison groups show that the program had significant positive effects on social competence for boys and girls in grade 5 and for girls in grade 6. Boys in grade 6 reported lower levels of externalizing problem behaviour compared to control students. There were no effects in regard to internalizing problem behaviour. The analysis also revealed that the results varied between classrooms. These results may be considered to add weight to the evidence in support of a wider implementation of the Second Step program.