Thursday, June 2, 2011

Followup on school choice in San Francisco

My previous post on how school choice is faring in San Francisco was called  School choice in San Francisco: a promise of transparency.  That promise still hasn't been fulfilled.

The idea was that, after the adoption by the school board of a New school choice system in San Francisco, SFUSD decided to implement the new, strategy-proof  "assignment with transfers" choice system itself (San Francisco school choice goes in-house).

School Board member Rachel Norton wrote in a November 9, 2010 blog post that
"Staff did pledge to make the documentation of the algorithm requirements and process flows public by February; I will continue to push to make the assignment algorithm itself open source."

While SFUSD has prepared a number of documents since then, none of them seem to contain a description of the SF school choice algorithm as actually implemented by the staff. All I can find are descriptions of the priorities used for tie-breaking if more children than can be accommodated by a school would otherwise have been assigned there, but no description of the process by which they would have been assigned before tie breaking has to be invoked.

The latest document of that sort, via Rachel Norton's June 1 blog post, is here: Board of Education Policy.
On page 7, under the heading "Method of Allocating Seats," the document states "The SFUSD will replace the diversity index lottery system with an assignment with transfers algorithm that uses school requests from families and the preferences outlined in this student assignment policy."
However the document doesn't describe the assignment with transfers algorithm at all, just the tie breaking priorities.

So...I'm still in the dark about whether SFUSD has actually implemented the choice system the Board adopted, and I bet SF parents and board members are too.
For those interested in the algorithm that the School Board adopted (and which may or may not have been implemented), here are some of the relevant links, in a quote from my "in-house" blog post linked to above.

Here is a post with a link to the video of Muriel Niederle presenting the new design that the Board ultimately voted to adopt: SF School Board Meeting, Feb 17: new choice system. 
And here is a link to the slides she presented, giving a description (with examples) of the new choice algorithm: Assignment in the SFUSD, and discussions of the features that make it strategically simple, non wasteful, and flexible.

In March 2010 the San Francisco Board of Education unanimously approved the new system. In their March 2010 press release, the SFUSD reported (emphasis added): 

"The choice algorithm was designed with the help of a volunteer team of market design experts who have previously been involved in designing choice algorithms for school choice in Boston and New York City. Volunteers from four prominent universities contributed to the effort, including Clayton Featherstone and Muriel Niederle of Stanford University, Atila Abdulkadiroglu of Duke University, Parag Pathak of MIT, and Alvin Roth of Harvard.
We are pleased that the district has decided to adopt a choice architecture that makes it safe for parents to concentrate their effort on determining which schools they prefer, with confidence that they won’t hurt their chances by listing their preferences truthfully,” said Niederle and Featherstone, the Stanford research team."

A very simple description of the basic assignment with transfer algorithm is given on page 370 of this paper (where it is called "top trading cycles"). Much of the SFUSD school Board debate has focused on what priorities to implement. What is described on page 370 is a simple version of the underlying choice engine into which the priorities go (with a somewhat different description than in Muriel's slides). The priorities can depend on any characteristics of the students (e.g. previous schools, or siblings, or home zip code) or of the school (e.g. neighborhood or historical student composition). But to keep the process strategically simple--to make it safe for families to rank schools according to their true preferences--the priority of a student at a school cannot depend on how that student ranked that school. (If you happen to be the programmer asked to implement this, drop me a line if you run into trouble:)

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