As wait lists for kindergarten seats become the norm at Upper West Side public schools, a handful of parents are campaigning for a real estate developer to hurry up and build a new school.

Their ad, which is being sent around but isn’t televised, asks parents to come to a community board meeting to demand that the Extell Development Company “build it first, build it big” — a reference to the public school Extell plans to build as part of its Riverside Center project.

Extell has already agreed to build a 150,000 square foot K-8 school, but when that would happen is still up in the air, said Community Board 7 member Helen Rosenthal. Rosenthal and others want a guarantee that the school will be located in the first building that goes up.