This study examines the hypothesis that the French used by a large number of Franco-Ontarians represents a linguistic system (or several systems) that differs from Standard French. In addition, a review of previous research leads to the inverse hypothesis, that Ontarian French represents a body of different systems or sub-systems that are more or less related to Standard French. It is proposed that Ontarian French is as valuable and efficient a communicative tool as is Standard French, when used among Franco-Ontarians in informal, everyday communication. The implications of this hypothesis are also examined with respect to: (1) interpretation of results on proficiency tests of Standard French, (2) development of further instruments to measure the proficiency of Franco-Ontarian students in French, and (3) development of classroom materials that focus on the particular needs of these students. (Author/AMH)