As Castilleja School moves ahead with its divisive expansion plan, project proponents often cite the long and accomplished history of the Palo Alto institution, which opened its Bryant Street campus in 1910 and which is now looking to rebuild it.

But on Thursday, it was the project's opponents who were touting the historical significance of Castilleja and its founder, Mary Lockey. The school's expansion plan calls for demolishing a home on Bryant Street that is named after Lockey. And though the home at 1263 Emerson St. has undergone numerous additions and modifications in recent decades and has not been deemed "historically significant" (Mary Lockey never actually lived there), several residents argued at the hearing of the Historic Resources Board that its removal could diminish the historic character of the school and the neighborhood.

Some argued that the recently released draft Environmental Impact Report (EIR) for the school's expansion should have included a full historic analysis of the home, as well of the neighborhood around the school. The board largely shared these concerns and, in doing so, added another wrinkle to the tense approval process that's been slowly making its way through city review.

Though board members didn't take a vote, they agreed that the Environmental Impact Report should further evaluate the Lockey house and the broader neighborhood for historic significance. As such, they requested that the analysis be revised as such.

The board's comments came less than a month after the city's Planning and Transportation Commission discussed the draft report and similarly found the document to be lacking. At its Aug. 14 meeting, the commission requested more information about traffic counts, bike routes and other design alternatives, including one that would not require the construction of an underground garage.

Thursday's hearing on the environmental analysis was far more subdued than the one last month, which brought hundreds of supporters and opponents of the Castilleja plan to City Hall. But much like at the first meeting, project proponents highlighted Castilleja's laudable mission of educating young women while opponents focused on potentially harmful impacts to the neighborhood.

Kimberley Wong, who lives on Emerson Street, was one of several speakers who brought up the Lockey Alumnae House and suggested that the structure should be preserved. The fact that this house is associated with a person of significance should qualify it for the National Historic Register, Wong said.

Andie Reed, who lives on Melville Avenue, argued that the report also failed to consider the historical significance of the residential neighborhood around Castilleja. The school's proposal would lead to both a change in land use and to changing traffic patterns — factors that she argued would alter the character of the neighborhood.

"Please recommend retaining the residential feel of our neighborhood and leaving this house intact," Reed said.

City staff, however, has taken the position that the house is not eligible for the California Register because of a "lack of integrity." A report from Planning Director Jonathan Lait notes that Castilleja had remodeled the home after acquiring it in the 1990s. The city's 1998-2000 historic surveyed found the home to be "potentially eligible" for the state register but not for the National Register.

Kathy Layendecker, associate head of school at Castilleja, said the all-girls school is "steeped in tradition" and that it has "created a clear and concise proposal that protects the historic elements of our campus through our project."

"The buildings we hope to replace have serve Castilleja well for 60 years," Layendecker said. "We want to create new places that will last even longer."

The project calls for reconfiguring about 84,000 square feet of academic space by demolishing seven existing buildings and building a three-story building with an underground level. The new campus would also have a 50,000-square-foot underground garage. As part of the project, the school is also proposing to increase its maximum enrollment from 415 to 540 students, with no more than 27 new students added each year.

But members of the board suggested that in evaluating future impacts, the consultants who studied Castilleja's expansion plan did not sufficiently consider the school's past. Board member Deborah Shepherd pointed to the "unique relationship historically between the school and the community.

"It's a very delicate balance. But it's a story worth telling, and we should be careful not to lose it," Shepherd said.

Board member Michael Makinen agreed. The school's contributions to education in the city constituted a significant "event" by state standards, potentially making the area worthy of recognition as a historic district, he said.

"All these things should be considered in the historic report. I don't think they're adequately addressed here," Makinen said.

The 60-day comment period on the EIR will conclude Monday. Comments can be submitted to Castilleja.expansion@cityofpaloalto.org.

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