Students from across New York City walked out of classes and marched for action on climate change Friday, joining young people across the world as part of the youth climate strikes.

Multiple protests were held across the city, including outside of City Hall, the Bronx High School of Science, Columbus Circle, and elsewhere. The young New Yorkers joined hundreds of thousands of students around the world demonstrating in the spirit of 16-year-old Greta Thunberg’s weekly protests in Sweden.

While public school officials said they encourage activism, students who skipped classes  Friday were marked absent. This differs from city policy during walkouts against guns last year, when the education department said students would only receive a notation on their attendance records only if they didn’t return to class afterward the protests.

“We encourage our students to raise their voices on issues that matter to them, and we also expect our students to be in attendance during the school day,” said Education Department spokeswoman Miranda Barbot.

Here are some tweets reflecting the students’ anger and outrage.