TORONTO -- Ontario's largest school board is weighing the costs of a full return to school come September, saying one model would come with a $250 million pricetag for elementary schools alone.

The Ministry of Education has given boards until Aug. 4 to provide back-to-school plans that take the COVID-19 pandemic into account, and the Toronto District School Board says some options come at a significant cost.

In a planning document, the board says if elementary students are divided into cohorts of 15 and there aren't any schedule changes, it will need to hire nearly 2,500 more teachers at a cost of $248.9 million.

The TDSB says if it cuts the school day by 48 minutes, it will only need to hire 988 teachers and the cost will be cut to $98.5 million.

Another option, which would see the youngest students in cohorts of 15 and older elementary students in groups of 20, would require just 200 additional teachers at a price of $20 million.

The board says that model would also see it cut French classes, because there wouldn't be enough staff to support them.

It also lists the possibility of returning with full class sizes, and a dismissal that's 48 minutes early.