School officials Thursday declined to identify the anonymous Palo Alto family who has proffered a potential donation of up to $20 million.
School board members Tuesday expressed enthusiasm for the preliminary designs, which were presented by architect Jeremiah Tolbert.
With architectural echoes of the older buildings on Paly's campus, the facility would include two new gyms on either side of the existing aquatic center that would be connected by a covered walkway evoking the open-air hallway which now connects Paly's Tower Building with Haymarket Theatre.
The proposed center — on an accelerated timetable because of the prospective donation — would have a June 2014 groundbreaking, with occupancy projected for August 2015. The school district would contribute $5.47 million.
In addition to the gyms, the new center would include a new wrestling/multi-purpose room, pool locker rooms and a new dance and yoga room.
Paly Principal Phil Winston said the new athletic center would "transform the experience" for students.
"This will change not just the physical landscape but the feeling on the campus at Paly forever," Winston said.
"It is something we need and could not be more thrilled about."
During construction, much of Paly's athletic program and many of its physical-education classes would be operated from portable classrooms now situated in the quad, officials said.
The portables, now in use by academic departments, will be vacated when a new, two-story, 27-classroom building opens over the winter break in December, they said.
Responding to the architect's drawings, school board member Melissa Baten Caswell said: "If it's completed and it looks like that, I don't think any district around us would be able to hold a candle. I don't think any of the private (schools) will be able to hold a candle."
Addressing equity issues raised by accepting a large donation directed at a particular school, board members said their general goal is "progressive parity" of student experience across the district.
Without the new Paly center, "the student experience for indoor athletics at Paly will not be of the same quality as indoor athletics at Gunn once the new Gunn gyms are completed," Caswell said.
"My goal is not how much money is put into each campus but that we have a parity of experience in volleyball, in basketball, in yoga and of course in all our core academics. It should be an equal experience."
Board member Barb Mitchell alluded to a high and growing demand for indoor athletic facilities at the high schools.
When Paly's existing gyms were built, "the only inter-conference sports for girls were tennis and swimming," she said.