With three teachers and 41 students in kindergarten through twelfth grade, Miss Ellis' School opened in rented quarters at 4860 Ellsworth Avenue.

By 1955, the year of Tilley's retirement, there were temporary classrooms across the street at Third Presbyterian Church, Hunt Armory, and the East Liberty YWCA.

The school purchased the 5.1-acre site at 6425 Fifth Avenue, part of the estate of Charles and Thomas Arbuthnot, where it remains today.

During her tenure, she created department heads and consulted with them on academic policies, allowed seniors to complete independent study and senior projects, brought visiting speakers to the school for weekly assemblies, and opened the school's facilities to the community.

In 1977, the school instituted the Experimental Intellectual Program (EIP) to provide funds to teachers for courses, conferences, curriculum planning, and travel.

In 1984, the school made the EIP permanent and renamed it the Janet Jacobs Enrichment Program (JEP).

The school occupied girls in the program from 3:15–5:45 pm with snacks, indoor and outdoor activities, homework, music, and art.

In 1990, the Ellis faculty started the Fifth Avenue Family Child Care Center, located in the basement of Arbuthnot House.

In 1974, the board approved plans for adding studio space and a new audio-visual room to the Fine Arts Building.

Goals included maintaining a low student-faculty ratio, keeping faculty salaries competitive, increasing population, and ensuring the proper upkeep of the physical plant.

Development II aimed to boost the book value of the Ellis endowment from two to four million dollars and increase annual giving.

Jacob retired in 1986, and Ellen E. Fleming, Ellis' new headmistress, arrived from Atlanta to oversee site preparation.

She began Symposia, which brought speakers such as columnist and writer Anna Quindlen, astronaut Sally Ride, researcher Carol Gilligan, and author Mary Pipher to address standing-room-only crowds.

Ellis held a $9.7 million Capital Campaign, which contributed to the construction of the Upper School Hillman Family Building, an increase in faculty endowment, a new alumnae hall, and a new athletic facility containing a regulation-sized gymnasium, climbing wall, and training center.

The Ellis Parents Association (EPA) works to help the school through volunteer programs and fundraising efforts.

Opportunities include Afghan Sister School,[9] Earth Cream Sale,[10] Environmental Ambassadors,[11] Guild,[12] and Mitten Tree.

[13] This Venture Program provides students with research opportunities in Pittsburgh's technology and medical labs, arts organizations, environmental sites, and global initiatives.

The school reviews applications in early September, and selected students work with Ellis administration and sponsoring organizations.

This capstone program provides a class trip to the Shakespeare Festival in Canada and requires a senior project.

Students may also take educational trips to various world destinations during March break or during the mini-course session in May.