Bottom line: while the size of the school stayed the same, the amount of students estimated for the school went up and then down, and the assignment of open space seems certain though it's been little discussed. (This may have been because the location of the school shifted.)
From the November 2006 Final Environmental Impact Statement, Chapter 19, Mitigation:
As stated above, the provision of a new P.S./I.S on the project site would partially mitigate the projected 2016 shortfall in school seats for schools located within ½ mile of the project site. While the school program and capacity would be developed at a later date, based on DOE’s average classroom size and standards for new school construction, a 100,000-gsf P.S./I.S would accommodate approximately 650 students, with approximately 270 seats for elementary students, 320 seats for intermediate students, and 60 seats for District 75 students (i.e., special education).(All emphases are added.)
The December 2006 General Project Plan indicated that a portion of the project's eight acres of "publicly accessible open space... may become reserved for use by the School during School hours... a small portion of which may be reserved for exclusive use by the School." The June 2009 Modified General Project Plan contained similar language.
The December 2009 Amended Memorandum of Environmental Commitments stated that developer Forest City Ratner "shall also provide to DOE [Department of Education], by lease, easement or other conveyance acceptable to DOE, access to suitable outdoor space for use as a playground for the School’s students." That's presumably part of B15 rather than the publicly accessible open space.
The June 2014 Final Supplemental Environmental Impact Statement, Mitigation chapter, stated:
While the final school program and capacity would be developed at a later date, based on DOE’s 2015-2019 Proposed Capital Plan, it is anticipated that this school would provide approximately 757 seats for elementary and/or intermediate students.The June 2014 Second Amended Memorandum of Environmental Commitments similarly referenced the need to provide "suitable outdoor space for use as a playground."
The May 2015 Notice of Filing (right) by the New York City School Construction Authority referred to a 616-seat planned school.
I haven't seen any explanation as to why the school capacity shifted up and down.
More recently, the SCA's January 2016 proposed Five-Year Capital Plan for the NYC Department of Education forecasted a capacity of 640 seats for P.S./I.S. 653 at the B15 site.