The chair of the Toronto District School Board says the province's controversial new sex-ed curriculum is partially to blame for declining enrolment.

The TDSB said on Thursday it will have to cut 100 teaching positions and make other staff reductions to deal with enrolment, which has been dropping steadily for a number of years.

Robin Pilkey told CBC Metro Morning's Matt Galloway the TDSB expects to have 3,500 fewer students next year, a number that includes 2,500 students they lost this year.

"The health and physical education curriculum had a hit on us this year and we're not sure how many of those kids will be back in the fall," said Pilkey.

That hit was due to children being pulled from schools by parents upset with the new curriculum, which came into force in the fall of 2015 amid protest from a vocal minority of parents across the province.

"We had a drop in the fall and this was discussed often, some kids came back and some kids didn't," said Pilkey.

Robin Pilkey, chair of the Toronto District School Board, believes parents are pulling their kids from school en masse because of the new sex-ed curriculum. (Robin Pilkey/Twitter) TDSB spokesman Ryan Bird told CBC News on Thursday that there are a number of factors causing school enrolment to fall.

"There are some neighbourhoods that 20 or 30 years ago may have had lots of families, and you see now it's mostly older people and not that many kids," he said.

Still, Pilkey thinks the sex-ed curriculum — which at various stages teaches about consent, masturbation, gender expression and the correct names for body parts — is a big part of it.

It's the first time the sex-education curriculum has been updated since 1998 and it sparked a lot of backlash from parents who believe it goes too far.

Pilkey said she hopes parents will change their minds next year when they've had more time to come to terms with the curriculum and realize it's not as extreme as they have been led to believe.

She added that enrolment numbers aren't yet final. If they improve by March, the TDSB might reverse the staff cuts.

If they do go forward, the school board hopes to avoid layoffs and make the cuts through attrition and leaves.