The Toronto District School Board says the words "shame on you" were sprayed on the walls of Thorncliffe Park public school and the neighbouring Fraser Mustard Early Learning Academy.
About half of the students at Thorncliffe Park were absent for the first day of classes Tuesday as their parents kept them out of school to protest the sex-ed curriculum.
The board says about 1,000 of the school's 1,400 kids are in classes today.
Wynne says vandalism is not civil protest and takes the opposition to the updated curriculum to "a whole different realm" that will require a police investigation.
She's also worried that little kids will be confused by the vandalism and by the anger among some adults about the first update to the province's health and physical education curriculum since 1998.
Wynne says she hopes things calm down in a very short time.
The premier says she's met with many of the parents in her riding who are opposed to the curriculum, but adds many did not know they could take their kids out of classes they object to for various reasons.
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