But while the debate got underway inside, outside hundreds of angry teachers marched to protest agianst Bill 115, which the Liberals used to force a contract on them.
The demonstration came just a short time after Premier Dalton McGuinty announced his government would go to the Labour Relations Board to prevent a one-day strike teachers on Friday.
Liberals will pick a new leader at a convention later this month, to replace the departing McGuinty, who has led the provincial party for the past 16 years.
The themes for Wednesday's debate were Toronto issues, education and the economy.
CBC Queen's Park correspondent Mike Crawley tweeted that since the questions are written by Liberal party members they "don't exactly hold candidates feet to the fire."
The seven people seeking the leadership are Eric Hoskins, Gerard Kennedy, Glen Murray, Sandra Pupatello, Charles Sousa, Harinder Takhar and Kathleen Wynne.
All seven candidates have cabinet experience under the McGuinty government, though two of the contenders — Pupatello and Kennedy — do not currently have seats at Queen's Park.
Since the start of the leadership campaign, the contenders have participated in four previous debates held in different parts of the province.
McGuinty announced in October that he was stepping down, though he agreed to stay on until a new leader was chosen.
His successor will inherit a party that has been in government for nearly a decade, but which has also struggled to be productive in a minority parliament.
And the new leader will also have to decide when to recall the Ontario legislature, which was prorogued when the premier announced his resignation.