"subject to School Committee allocation"
You might not get this from the press coverage, but the memo from Superintendent Boone to City Manager O'Brien is a set of recommendations to the School Committee. It doesn't happen until it's passed by School Committee; that's not just pro forma, either, as the Committee has been known to make changes.
Also, as I added in my notes last night: it is the City, not the Schools, that build schools. They run the show when it comes to things including the size of parking lots.