Neighborhood House Charter School (NHCS) has filed plans with the Boston Planning and Development Agency to add 12 classrooms and a gym in a three-story extension to its Pope’s Hill school. One of the oldest charter schools in the state, NHCS says its expanding number of students means the current building on its 2.3-acre site at 21 Queen St. is no longer big enough.

The school plans to finance the roughly $12-million project through a combination of fundraising and borrowing. It hopes to begin construction in March of next year, with the new space ready for students by the end of June 2021.

In its filing with the BPDA, the school explained the need for the new classrooms, gym, and changes to the way traffic flows into and out of the site.

“The building is not large enough to house the 8th grade, causing them to be located off-site approximately one mile away,” the filing reads. “The building has several smaller classrooms where columns obscure instructional sightlines. The building has no indoor recreation space. When weather prevents students from playing outside, recess and physical education take place in hallways – which is both limiting to students and distracting to instructional settings nearby. Current parking is tight, and several staff routinely park on residential streets nearby, frustrating neighbors. Finally, current traffic queuing during drop-off and dismissal times creates challenging situations for the nearby residents.”

Neighborhood House, which started in 1995 with 51 students, today has 650 students, a number it plans to increase to 828, following state approval three years ago to open a high school. The first high school seniors are expected to graduate in 2021.