The first separate school opened in Coniston on October 9, 1913 with 107 students filling two of the three available classrooms. By the start of the fall term in 1914, the third classroom was also in use. Two years later, in 1916, over 215 children were enrolled in the separate school and there was not enough classroom space for them all. So the school board made arrangements to rent a vacant classroom from the public school. This arrangement last until 1921 when the public school required the return of its classroom to accommodate its own student growth.

In the summer of 1921, a new cottage was constructed on Second Avenue to serve as a fourth classroom for the separate school. By 1923 and 1924, two additional cottages were built, bringing the total number of separate school classrooms to seven.

As the population in Coniston continued to grow, school enrollment was also increasing, which resulted in a difficult situation for the school board trustees. In 1925, there was no more room on the school's property to build additional classrooms and the playground could not hold any more children, so the school board appealed to the Mond Nickel Company for assistance. The company responded by providing the school with a nine-acre lot at the end of Edward Street on which the trustees could build a two-storey brick school containing ten classrooms and a full basement. The basement of the school served to provide students and the public with an auditorium and a stage for use in school concerts, church events, public dances, and various other social activities for the community. This new school became known as Our Lady of Mercy (or École Notre Dame de la Merci). The former separate school on Balsam Avenue was subsequently transformed into the Coniston Continuation School and the four cottages that were built were renovated into private residences for employees of the Mond Nickel Company.

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