Parents at public schools on the Upper East and Upper West sides of Manhattan are being asked to donate as much as $1,500 a child to hire additional teaching assistants for city classrooms.

Faced with large class sizes and a desire to attract more middle-class families, parent associations are kicking into gear and asking for considerable sums.

Because many of these schools attract parents who could otherwise afford private education, they struggle to provide some of the same amenities.

Kindergarten parents at P.S. 166 on West 89th Street, for example, are asked to donate $1,500 a child to hire assistants. Parent association members at the school point out that the amount is only suggested and nobody is pressured to pay more than they can afford; the donation is also kept confidential.

“I knew that having another person in the classroom would make a big difference and it made me feel a lot more comfortable,” a vice president of the PTA at P.S. 166, Jolie Kapelus, said. A lawyer who is now a full-time parent with two older children in private school, Ms. Kapelus said the assistant was a large factor in her choosing the school for her child.

Other schools, mostly on the Upper East and Upper West sides of Manhattan, also ask for hefty donations. Many parents were reluctant to discuss the practice, fearing that by making it public they risk having the Department of Education step in to stop it.

While the majority of funding is typically generated from the gifted and talented classes at P.S.166, parents said the PTA is firm in its commitment to providing assistants in all classrooms.

At the highly selective Anderson School on West 84th Street, a public school that broke off from P.S. 9 in 2005 to become its own school, parents are asked to contribute about $450 a child. In addition to putting assistants in the classroom, the money goes toward other enrichment programs such as Spanish classes.

At the highly regarded P.S. 6, located just blocks from the Metropolitan Museum of Art on the Upper East Side, parents are asked to contribute about $600 a child to place assistants in kindergarten and first-grade classrooms. In addition, all parents in the school are asked to contribute $350 a year, according to “New York City’s Best Public Elementary Schools: A Parents’ Guide,” by Clara Hemphill.

At the nearby P.S. 158, parents are asked for about $500 a child, according to the book. Parents at the Lower Lab School on Third Avenue and 96th Street receive appeals asking for about $900.

Parents point out that without the assistants, a teacher would be left to contend with about two-dozen 5-year-olds. Still, not all schools agree with the practice.

Sandra Bridges, the principal at P.S. 234 in TriBeCa, where students’ test scores are among the highest in the city, said the class sizes have always been large and that encourages students to become independent. She also said having the PTA become an employer might cause more headaches than it’s worth.

The city Department of Education employs about 17,000 school aides, known as paraprofessionals, although the majority of them work with special education students. Unlike the paraprofessionals, assistants are not members of the teachers’ union and earn about $10 an hour.

The schools doing the most fund raising tend to be disproportionately white and middle-class. Some parents said the lack of poor children in those schools actually makes the fund raising more necessary, because federal funding follows low-income students.

“If a school is classified as Title I, the funding is coming in up the wazoo,” a PTA co-president at the Anderson School, Christine Cirker, said. “That’s the hitch of bringing in middle-class families, you’re basically penalized so you have to fund-raise.”

Under the U.S. Department of Education’s Title I program, funds are made available to help low-achieving children in high-poverty areas.

Eva Moskowitz, the former chairwoman of the City Council’s Committee on Education and a public school parent on the Upper East Side, said fund raising from parents is fairly commonplace in middle-class neighborhoods. She said parents shouldn’t be punished for wanting to contribute to their children’s education.

“We have to figure out ways to have more equity in the system, but I don’t think you want to take away parents’ ability to give money when the system isn’t doing its job,” she said.

Under the chancellor’s regulations, money raised by parents can be used to hire support staff but not a lead teacher for the classrooms.

A spokeswoman for the Department of Education, Kelly Devers, said, “Contributions must be given voluntarily and there can be no coercion. A hint of coercion and the chancellor would not approve it.”

The education author, Ms. Hemphill, called the system “unfair.”

“I think the gross disparity between city and suburbs is really unfair, and the gross disparity between upper-middle-class neighborhoods and poor neighborhoods is really unfair.” Ms. Hemphill said.

“If you ask middle-class parents in Manhattan, they say that even with this money our schools are still underfunded compared to the suburbs and certainly our children are less privileged than the kids at private schools. But I don’t blame the well-off parents for trying to get decent schools for their kids.”