This study is the first to investigate education outside the classroom (EOtC) and pupils’ social relations in a large-sample experimental design. Social Cognitive Mapping was used to collect data on informal peer affiliation groups among pupils, aged 9–13 years, at the start and end of the school year. 332 pupils from 16 classes that were regularly exposed to EOtC, were compared with 158 pupils from 8 comparable classes that were not. Regular exposure to EOtC was positively associated to a gain in new peer affiliations, but not to increases in the total number of relations. In conclusion, regular exposure to EOtC is related to minor positive changes in pupils’ informal peer affiliations in their class networks.