One million free children’s books have been mailed to D.C. families since the city partnered with famed country singer Dolly Parton three-and-a-half years ago on her national initiative to promote early literacy.

The D.C. Library’s “Books From Birth” program—which sends enrolled kids a free book every month until their fifth birthday—hit the milestone in August, prompting Parton to call it a “remarkable achievement to celebrate” in a letter to city officials. Almost 35,000 children across the city are currently registered to receive books through the program, which kicked off in early 2016.

“That we’ve been able to hit one million books probably faster than any municipality I know that has implemented a similar program means there’s a thirst for early literacy in the city,” says Rich Reyes-Gavilan, the executive director of the D.C. Library.

The program is part of Parton’s Imagination Library, which she launched in 1995 to promote reading among children. While it originally only served kids in her home of Sevier County, Tennessee, it has since expanded to dozens of counties and states across the U.S. (including Alexandria, Virginia and Prince George’s County in Maryland), as well as programs in the United Kingdom, Australia, Ireland, and Canada. Last year, Parton celebrated her 100 millionth book delivery at the Library of Congress; this August, the total number of books delivered jumped above 125 million.

The logic behind the program is simple: research shows how much the brain expands during the first five years of life, and reading to children has been shown to help improve their educational development and outcomes. That’s what motivated Ward 6 Councilmember Charles Allen when he introduced the bill in 2015 bringing the “Books From Birth” program to the city.

“I was working on trying to come up with some ideas around ways to address the literacy gap that we see, and I happened to go down to visit my brother and his family down in Tennessee. We were sitting around and all of a sudden the mailman shows up and my niece goes running to the mailbox and there’s a book,” he says. “I had a really strong hunch this would be really impactful.”

Both Allen and Reyes-Gavilan say that a key element of the program’s success was ensuring the books went to children who would most benefit from receiving them—those in the city’s lower-income neighborhoods. And that meant aggressive outreach to make sure that families signed up to get the books delivered.

“It’s important for us to do outreach in Wards 5, 7, and 8 because we want to contribute to the elimination of the achievement gap. We are firm believers that literacy from an early age and getting kids reading at grade level is a key to equity,” says Reyes-Gavilan.

According to the D.C. Library, those wards rank among the highest in the number of book deliveries since the program started. While Ward 4 leads with 180,767 recipients, Ward 8 came in second at 169,007, followed by Ward 5 at 156,369 and Ward 7 at 153,568. Ward 2 and 3 had the fewest books delivered, at 48,820 and 77,284, respectively.

The books that are sent monthly are chosen by the Imagination Library, an arrangement that Reyes-Gavilan admits initially gave him pause. But he says he has been happy with the selection of books, which have included bilingual titles and books like A Snowy Day, which dates back more than 50 years and broke ground at the time by including a black character. Allen, whose two children have received the books, also appreciates the diversity of the offerings.

“There’s something incredibly powerful about the fact that every kid in D.C. can see themselves in the pages. It’s an incredibly diverse array of books, there’s different languages, kids of different backgrounds. My hope is every single child will see themselves in the pages of these books,” he says.

And Reyes-Gavilan says the program—which costs D.C. just under $1 million a year—can have a secondary benefit: increasing visitors to the city’s neighborhood libraries, many of which have been modernized in recent years.

“The biggest complaint that I get about this program is that it stops at age five,” adds Allen. “The number of five year olds that are upset when they get their last book really makes the case we should keep this going. But that’s why we have beautiful libraries ready for them. We want to get them in those doors.”

This story originally appeared on WAMU.