[Live coverage of the climate strike in New York City.]

Hanna and Kian Joulaee, twins and fifth graders at Public School 10 in Brooklyn, spent Wednesday night decorating signs and T-shirts for a rally in Red Hook set for Friday, a day of global youth protests for urgent action on climate change.

But on Thursday morning, their mother, Tannaz Fassihi, received an email from school administrators, explaining, “with a sense of disappointment,” that the optional field trip to the rally was canceled.

The city’s Education Department ruled that employee participation would violate rules ensuring a “politically neutral learning environment,” as would schools that stage their own climate-action walkouts on school property.

Ms. Fassihi was crestfallen. As an Iranian-American who grew up in Tehran unable to freely express opinions, she said she had been excited to see her children’s school teaching civic engagement by example, along with teaching about climate science.