It was the first day of school Thursday for the city's 1.1 million public school students. The mayor and schools chancellor used the occasion to push their sweeping education agenda. NY1's Lindsey Christ filed the following report.

Students - some striding, some skipping, some slogging -  made their way to public school Thursday morning. 

"I like school, so I really wanted to go back to school," said Paris Edie, a third-grade student at PS 156.

Mayor Bill de Blasio and Schools Chancellor Carmen Fariña hit the sidewalks, too, escorting seventh-grader Chyna Huertas to IS 392 in Brownsville, Brooklyn, the mayor's first stop on his annual five-borough school tour. 

For the past two years, the mayor has used the first day of school to celebrate universal pre-kindergarten, a signature education initiative. This year, he chose to highlight the rest of his education agenda. That includes expanding mental health services, requiring Advanced Placement courses in all high schools and, within 10 years, having all third-graders read on grade level and every child study computer science.

"Educators will tell you also that is extraordinarily ambitious that is going to take everything we know how to do and then some. And a lot of resources."

The clock is ticking for 86 struggling schools required to show progress by June. The mayor and chancellor say they're now willing to close schools that haven't improved enough. 

"It's really just a few that for whatever the reason are not going to move in the right direction," Fariña said.

A few miles away, a high school student was arrested trying to bring a loaded pistol into the Brooklyn School for Career Development. The union representing school safety officers seized on the incident in accusing de Blasio of wanting to remove metal detectors from some schools. 

There is a plan to evaluate in schools where the school community itself thinks that either the scanner should be subtracted or added or changed, that that can be evaluated by both the educators in the public safety officials. 

Pre-k wasn't completely off the agenda. At a pre-k school in Queens, the mayor announced that more than 70,000 students were registered for pre-k, five thousand more than last year and fifty thousand more than three years ago.