Mayor Bill de Blasio is being pressured to go from universal Pre-K to universal free lunch for all city students.

All five of the city's Borough Presidents have signed a letter to the mayor asking him to set aside money in next year's budget to provide free lunch at every public school in the city.

Many kids already qualify for free or reduced-price lunch based on their income, but universal lunch supporters say this stigmatizes students, with some going hungry because they're too embarassed to accept food for free while others still have to pay.

In the letter to de Blasio, all five borough presidents say a well-fed student performs better, saying "The schools that offer universal free lunch see an increased participation rate across all grade levels, including a 15 percent difference in high school, a 20 percent difference in middle schools, and a 10 percent difference in elementary schools."

A pilot program to offer free lunch at city middle schools is already underway, and the Mayor's Office says it is looking into the possibility of expansion.