TORONTO -- More Ontario elementary teachers are starting strike action even as another school board has reached a tentative deal with high school teachers.

The Ottawa-Carleton District School Board was the latest to hammer out a tentative agreement early Thursday morning -- making it the eighth board to have struck a deal, said the Ontario Secondary School Teachers' Federation.

Six of those deals -- at York Region, Upper Grand School District, Thames Valley, Avon Maitland, District of Niagara, and Hamilton-Wentworth District school boards -- have been approved by the government so far.

The Durham school board is still waiting for the green light.

Teachers in about 20 other school boards are still in a legal strike position.

The OSSTF said details of the deals will remain confidential until the agreements are ratified.

"These tentative agreements show what's possible when we continue to work with our partners to find solutions," Education Minister Laurel Broten said in a statement.

Many high school teachers started strike action Nov. 12 after the OSSTF failed to reach a last-minute deal with the governing Liberals. It includes not attending staff meetings, not communicating with parents outside school hours or filling in for absent colleagues.

Now more elementary teachers are set to join them.

About 5,000 teachers at York Region were the first to take strike action on Monday, and were joined by about 134 teachers at the Rainy River District School Board on Thursday.

About 1,111 teachers at the Trillium Lakelands District School Board and 1,340 at Kawartha Pine Ridge are poised to start work-to-rule next Monday, according to the Elementary Teachers' Federation of Ontario.

The job sanctions include arriving no sooner than 30 minutes before class starts and leaving no later than 30 minutes after students are dismissed. ETFO also advised all of its members about a month ago to write only the bare minimum on report cards.

While the two unions insist that withdrawing from administrative duties won't affect student learning, concerns have been raised about safety.

The Ontario Principals' Council said the only way to ensure that students are safe is to have an adequate number of teachers and trained adults supervising in the school. Safety would be jeopardized if supervision is withdrawn, or on-calls for absent teachers aren't covered, it said.

OSSTF, which represents 60,000 members, and ETFO, with 76,000 members, are protesting the Liberal government's anti-strike law, which also cuts benefits and freezes wages for most teachers.

Four unions are taking the government to court, arguing the law is unconstitutional and violates collective bargaining rights.

Bill 115, which passed with support from the Progressive Conservatives, gave the government the power to stop strikes and lockouts, but the minority Liberals haven't exercised it yet.

They can also impose their own agreement if they don't like what the unions and school boards negotiate together.

Broten has said that any tentative deal must be "substantially identical" to the one it struck with English Catholic teachers in July.

It froze the wages of most teachers and cut benefits, such as the banking of sick days that can be cashed out at retirement. A similar deal was reached with francophone teachers.