The District offers free full-day preschool to 3- and 4-year-olds through a lottery each year. Families enroll where space is available, sometimes driving miles from their homes to take advantage of the benefit.

But when the enrollment lottery opens Dec. 15, five elementary schools will for the first time offer guaranteed preschool admission to families within their attendance boundaries.

The schools are part of a pilot to begin implementation of a policy, approved by Mayor Vincent C. Gray (D) in August, related to the overhaul of school boundaries.

“The new policy is an opportunity to make the pre-kindergarten process less stressful, by adding predictability and making what used to be a preference into a right,” according to a new boundary implementation plan.

The plan offers a road map for the rollout of the new school boundaries and 42 related student assignment policy recommendations. Schools Chancellor Kaya Henderson released the plan just days before the election, offering more timelines and specifics just as a new mayor is about to take the helm, a transition that could cast the plan into uncertainty.

Gray authorized new school boundaries to take effect in the 2015-2016 school year. Council member Muriel E. Bowser (Ward 4), the Democratic nominee for mayor, responded that the plan is “not ready” and vowed to restart the boundary discussion. Council member David A. Catania, (I-At Large), another mayoral candidate, said he would pause the process for a year to explore its implications. Independent candidate Carol Schwartz has said she would make some changes to the plan but would not start over.

The plan represents the first comprehensive overhaul of the city’s school boundaries in more than 40 years and was developed through a 10-month, emotionally charged community process. Residents have worried about how the new lines will affect their children’s academic opportunities or the value of their homes in a city where school quality varies dramatically. Others are relieved to see a more coherent plan for assigning schools and dealing with crowding and under-enrollment.

“The implementation is moving forward, but there’s still a question: Can they undo it?” said Faith Hubbard, a member of the citizen advisory committee that worked to develop the plan.

The office of the deputy mayor for education, which developed the plan, says it is “not a final draft” but something that will be updated based on “feedback, progress and new developments.”

Some changes already are in motion.

Boundary maps are being updated for the online enrollment lottery and application system, and when it opens on Dec. 15, parents who are new to the school system will enroll their children based on the new boundaries.

Extensive grandfathering provisions are included for families who are enrolled in city schools. All 23,100 students who currently attend their zoned school will be able to remain, even if their address is reassigned to a new school.

Students in third grade or higher have the option of continuing through the middle schools and high schools they plan to attend. Younger students will be rezoned into their new middle schools and high schools unless they have a sibling attending their former school at the time they will be there.

Only a few of the related policies would take effect next year.

Students enrolled in a Science, Technology, Engineering and Math program at McKinley Middle School will have the right to feed into a similar STEM program at Woodson High starting next year, part of an effort to create school feeder patterns based on programs and not just geography. And those who live more than a half-mile from their assigned school will receive a preference in the lottery for another school if it is less than a half-mile from their home, an effort to encourage walkable routes to school.

Most of the policies would go into effect later, if at all. For example, the boundary plan calls for reopening four middle schools to address demand for more quality middle schools. The implementation plan does not offer a budget or timeline for the opening of three of those schools, but says a schedule and relevant costs will be proposed next spring.

The pilot program to give families guaranteed access to preschool in neighborhood schools would eventually expand to include all Title I — or high-poverty — elementary schools. It is an effort to encourage families to start and stay with their neighborhood schools. But implementing it more broadly will be challenging and could take years to build up capacity, according to the plan.

The schools included in the first-year pilot are Burroughs Education Campus and Brookland Elementary School in Ward 5; Amidon-Bowen Elementary School and Van Ness Elementary School in Ward 6; and Stanton Elementary in Ward 8.