Plan B emergency contraception is about 90 percent effective at preventing pregnancy if taken within 72 hours after unprotected sex.
New York's program was phased in at health clinics at about 40 schools in the 1-million-student school system starting about four years ago. Since January 2011, it has expanded to 13 additional schools that don't have clinics. The little-known program was reported on Sunday by the New York Post.
Nurse practitioners or physicians dispense the pills, and parents can sign an opt-out form preventing their daughters from taking part. Only about 1 to 2 percent of parents have opted out, according to the city Health Department.
The program is seen as a way to reduce a startling number: More than 7,000 New York City girls ages 15 to 17 get pregnant each year. More than two-thirds of those pregnancies end in abortions.
"We are committed to trying new approaches ... to improve a situation that can have lifelong consequences," the Health Department said in a statement.
In the 2011-12 school year, 576 girls got the pills at the 13 added schools, said Deborah Kaplan, an assistant health commissioner.
"I do think it's a good idea," she said. "The children nowadays are not going to abstain from sexual intercourse. How many unwed mothers do we need?"