For over forty years, presidents of the Summer School Association of Queen's University wrote annually to teachers across Canada, encouraging them to attend summer courses for credit toward a bachelor of arts. In the 1920s, presidents' messages associated attendance with societal progress and the professionalization of teaching. In the 1930s, such messages linked attendance with personal growth and career development. In the 1940s and 1950s, they linked attendance with having an enjoyable summer vacation. This article analyzes how and why these messages evolved and argues that the underlying structure of the messages remained consistent: they were means through which Queen's Summer School Association presidents marked symbolic boundaries between more and less professional teachers. This article contributes to our understanding of the social history of teacher education by interpreting a unique primary data source to explore the participation of teachers themselves in the construction of symbolic boundaries marking professional status.