Superintendent Kevin Skelly disclosed the March 13 offer at the Board of Education meeting Tuesday night.
Summerhill Homes — which in 2011 obtained City Council approval to build 10 homes on the site — has given the school district until March 27 to decide on its all-cash offer for the property, which is contiguous with district-owned land at Greendell School and Cubberley Community Center.
The property was home for nearly 40 years to the Peninsula Day Care Center, which closed its doors in June 2011 when the owner retired.
The school district bought the parcel in late 2011, disrupting a contract between Summerhill and owners of Peninsula Day Care.
But Summerhill proceeded to secure city approval for housing development in case the school-district purchase fell through.
The district has been leasing 525 San Antonio on a short-term basis to a private school for children with dyslexia.
The property, combined with the Greendell campus at 4120 Middlefield Road, is under consideration by a citizens committee currently evaluating possible locations for a 13th elementary school. That committee, whose report is expected this spring, has been told to weigh tradeoffs between opening a school at Greendell/San Antonio or at the former Garland Elementary School at 870 N. California Ave.
Skelly did not hint that the school district was engaged in any negotiations with Summerhill.
"I am pleased that the board had the foresight to make this purchase," he said. "While I deeply worry about what this price suggests about the future of our community to be economically diverse, I do feel that the increased value reflects well on the work of the schools in our community."
The San Antonio parcel was excluded from consideration by another citizens committee that spent the last nine months analyzing options for the 35-acre Cubberley Community Center. Twenty-seven of those acres are owned by the school district and eight are owned by the City of Palo Alto.
At the time the school district purchased 525 San Antonio, leaders were worried that enrollment was growing faster than expected.
They also were mindful of now-regretted school-district decisions 30 years ago to sell off sprawling elementary school campuses — closed because of declining enrollment — for housing developments.
At its peak in 1969, Palo Alto school enrollment stood at 15,000 before dropping to a low of about 7,500 in 1989. Since then it's been on an upward trajectory and currently stands at about 12,350.
In 1976, the school district sold Ortega Elementary School for $2.5 million and Ross Road Elementary School for $3.6 million. In 1979 it sold De Anza Elementary School for $2.7 million.
In 1981 it sold Crescent Park Elementary School for $4 million and Hoover Elementary School (then on Middlefield Road across from Midtown Safeway) for $2.8 million. Most were developed into housing.