If you take TTC, It's my proposal:
1) Anyway you go to Islington subway station.
2) In Islington Subway station, Take (Mississauga)TTC Bus 110 A/B to "Long Branch"(a transit center).
3) Take Mississauga TTC Line 23 to the school ( you can ask the driver or people on the bus that which stop you should get off. (at IBar road)