TORONTO -- The Canadian Press has learned that Ontario will put $1.6 billion toward ensuring school boards don't have to lay off teachers as a result of increasing class sizes.

Senior government sources say the attrition protection money will be announced Friday, along with school board funding allocations known as Grants for Student Needs.

The sources say that school board funding will increase from last year, though "not massively."

The Progressive Conservative government has announced that high school class sizes will increase, from an average of 22 to 28, over four years.

School boards have said that will mean thousands of teaching jobs are lost, but Education Minister Lisa Thompson has said that will be done through attrition, and no teacher will "involuntarily" lose their job.

The government sources say the $1.6 billion will mean that if a school board has 10 fewer retirements than expected, for example, it can afford to not lay off 10 teachers by drawing on the fund.