TORONTO -- A work-to-rule strike by Ontario's public elementary school teachers means they are not participating in training on the province's new sexual-education curriculum.

Schools remain open and extracurricular activities and field trips continue for now, but teachers won't administer standardized tests, add comments to report cards or participate in any professional development related to Ministry of Education initiatives.

The president of the Elementary Teachers' Federation of Ontario says that includes training on "any new or revised curriculum document, including the revised health and physical education curriculum."

Sam Hammond says the union supports the new curriculum, but the work to rule will continue until the government takes what he calls "offensive concessions" off the table.

The sex-ed curriculum was last updated in 1998 and the new version, which will be taught in schools starting in September, has prompted thousands of parents to protest, saying the material is not age appropriate.

Education Minister Liz Sandals says it would be preferable for teachers to attend professional development on the new curriculum, but if not, "they'll have more work to do over the summer on their own" to prepare.

Each year the ministry focuses professional development on a few areas, and this year it's math, closing the gap for aboriginal learners and the updated health and physical education curriculum, Sandals said. Right now the training is at the "board team" stage and those board teams then do professional development with teachers. Most board teams also include some teachers.

Sandals said she is concerned the work to rule is not simply administrative, but is affecting students.

"We're calling on the elementary teachers to stop interfering with work that's really important to the future of our students," she said.

The elementary teachers' work-to-rule is happening at the same time as high school teachers at three boards are on strike. Ontario's Labour Relations Board will hear an application Thursday from the three boards asking for the strikes to be declared illegal.

More than 70,000 students have been out of class for weeks and the school boards in Durham Region, Rainbow District, which includes the Sudbury area, and Peel Region say the strikes are unlawful.

The boards believe the Ontario Secondary School Teachers' Federation is staging local strikes on central issues, which is not allowed under a new bargaining system the Liberal government introduced last year. It separates local and central negotiating, with issues such as money and class sizes being discussed at the provincial table.

The local unions deny the school boards' assertion that the local strikes are just part of an overall provincial strategy to put pressure on the government.