By the year 1927, the population of Oshawa had greatly increased due to the coming of manufacturing plants. The number of pupils in the separate school was now 250. The school could not accommodate all who wished to attend. Rev. Father P.J Bench was faced with the problem of finding classroom space. He was a powerful advocate of education in Catholic schools and was also the Separate school representative on the Protestant Board of Education, for the Catholic secondary students. In January 1922, when the Catholic school board met, he discussed the problem of over-crowding with them. The trustees at that time were as follows: R. Smith, D. O’Brien, J.J. Mullen, F.J McDonnell, J.S. O’Brien, L. Le Fave, W. Hambly, J.F. Bruke, Rev. P.J. Bench.
In the year 1927, under the guidance of Father Bench an addition was built on the school. It then had ten classrooms, a spacious auditorium, play rooms, a medical room, teachers’ rooms and a kitchen. Also by that time owing to a steady income, six teachers were hired to assist the Sisters in their work. Five out of the six teachers employed had obtained their first class teaching certificates and were being paid $725 per year. There were about 400 children in attendance.
The principal in Jubilee year, 1927, was Sister Margaret Mary. She is the sister of Mrs. Leo Karnath, who is residing in Oshawa at the present time, and was principal of St. Gregory’s school for eight years. She is at present in St. Joseph’s convent in Toronto. She celebrated her Diamond Jubilee (60 years) in 1963, in St. Joseph’s order.
By the year 1930, the Oshawa separate school attendance stood at 454. The average was only 75%. This was an important factor as the legislative grant was based on daily attendance and not on the total enrolment as it is now.
 Pedlar People Ltd, Ontario Malleable Iron Co., McLaughlin Motor Car Co., Fittings Ltd. had been well established for decades by this point.