I've written before about school choice in San Francisco, and about how Muriel Niederle and Clayton Featherstone led the effort by a group of our colleagues to design a strategy-proof choice algorithm (explained here at a Board meeting in 2010), based on transfer cycles ("top trading cycles" to game theorists...). The school board adopted the plan, but then the staff of the school district decided to implement it themselves, without making the details public. Fast forward to 2012, when the first children have been assigned by the new plan.
Rachel Norton's blog has a post about it here: They're out! School Assignment Letter 2012, and an earlier one here, with a link to a March 5, 2012 SFUSD report on Student Assignment. As in the previous SFUSD reports, this does not describe the choice algorithm, it only describes the "tie breakers" that are used whenever the algorithm would otherwise try to assign more students to a school than it has room for.
This outraged Stan Goldberg (who reports about SF schools as "Senior Dad"), and he posted a video about the lack of transparency called Assignment System Fraud?
He must be an influential guy, because this prompted SFUSD to post some new information, including this "fact sheet" dated March 23, called How does the student assignment computer program work? It still doesn't come close to explaining the actual algorithm they use, but it does include a diagram of "transfer cycles."
Which raises a question. If they in fact implemented the plan we proposed and the Board adopted, you would think they would want to make this clear. The benefits of a strategy-proof assignment procedure can only be realized if parents know that they can safely list their true preferences.
On the other hand, if the algorithm isn't correctly implemented, or if some other assignment algorithm is implemented (whether or not it includes some use of transfer cycles) then it would most likely not be strategy-proof, that is, it might not be safe for parents to reveal their true preferences, and it might be in the interest of some to "game the system" in some way. That might account for a desire to keep the algorithm secret. (So might a desire to avoid revealing any inadvertent mistakes in implementation...)
I should say that SFUSD's brief description of their algorithm doesn't look to me like it describes one that is strategy-proof...:(On the contrary, it looks like it might be patched together from something like Boston's old immediate acceptance algorithm followed by some trading...but then again, it isn't a complete enough description to make me confident that it is a description of whatever they are in fact doing...)
Anyway, one point of this post is to say that, unlike the case of the systems in New York and Boston and the work that IIPSC is doing around the country, my colleagues and I don't know what algorithm SFUSD is using, even though we know what we proposed and the Board adopted. So...this post is a bit like the ads that sometimes appeared in the financial sections of newspapers when I was young, which, following a divorce, would announce that Mr John Doe was henceforth no longer responsible for any debts incurred by the former Mrs John Doe...