Rivers was assigned to Purcell High School after his ordination in 1956, along with part-time parish ministry at St. Joseph Church and Assumption Parish. Purcell at that time was a predominantly white, all-boys high school, and Rivers was the only Black faculty member. During his ten years at Purcell, he taught several subjects including English, Drama, Philosophy, and Literature, and he served as Chair of the English Department. In his writings, Rivers said that it was his love of the theater, which he attained under the tutelage of a beloved seminary professor, Monsignor George Berwanger, that inspired him to reestablish the school's drama club with Brother Ray McQuade, naming it the "Queen's Men." The ensemble became a critically acclaimed semi-professional acting group. Rivers and McQuade took students to the Stratford Shakespeare Festival in Stratford, Ontario once a year. Rivers also mentored and coached students to state championships and awards in literature and drama.